diff --git a/frontend/src/capture/PhotoStage.svelte b/frontend/src/capture/PhotoStage.svelte
index 70e2cb3..7b003c2 100644
--- a/frontend/src/capture/PhotoStage.svelte
+++ b/frontend/src/capture/PhotoStage.svelte
@@ -2,9 +2,11 @@
   import { onDestroy, onMount, tick } from 'svelte';
   import type { BBox } from './capture.types';
   import { fitDisplay } from './fitDisplay';
+  import { decodeOrientedBitmap } from '../decodeOrientedBitmap';
 
   // Display-only: renders the photo fitted to device width (height capped) plus
   // one overlay layer. All math lives on source pixels, not this canvas.
+  // Geometry must use the same EXIF-oriented bitmap space as the mask worker (#72).
   export let blob: Blob;
   export let maxH = 420;
   export let bbox: BBox | null = null;
@@ -12,21 +14,12 @@
   export let maskW = 0;
   export let maskH = 0;
 
-  let url: string | null = null;
   let canvas: HTMLCanvasElement | undefined;
   let stage: HTMLDivElement | undefined;
-  let imgW = 0, imgH = 0; // source px, learned once per blob
+  let imgW = 0, imgH = 0; // source px (oriented), learned once per blob
   let parentW = 0;
-
-  const setBlobUrl = (b: Blob) => {
-    if (url) URL.revokeObjectURL(url);
-    url = URL.createObjectURL(b);
-  };
-
-  $: if (blob) {
-    setBlobUrl(blob);
-    imgW = 0;
-  }
+  let decodeGen = 0;
+  let decoding = false;
 
   const applyFit = () => {
     if (!canvas || !imgW) return;
@@ -37,73 +30,83 @@
     canvas.style.height = `${fit.fitH}px`;
   };
 
-  const redraw = () => {
-    if (!url || !canvas) return;
-    const ctx = canvas.getContext('2d')!;
-    ctx.clearRect(0, 0, canvas.width, canvas.height);
-    const img = new Image();
-    img.onload = () => {
-      if (!canvas) return;
-      imgW = img.width;
-      imgH = img.height;
+  const paintOverlays = (ctx: CanvasRenderingContext2D) => {
+    if (!canvas) return;
+    if (maskBitset && maskW > 0 && maskH > 0) {
+      const off = document.createElement('canvas');
+      off.width = maskW;
+      off.height = maskH;
+      const octx = off.getContext('2d')!;
+      const d = octx.createImageData(maskW, maskH);
+      const tile = 8;
+      for (let p = 0; p < maskW * maskH; p++) {
+        if (!maskBitset[p]) {
+          const x = p % maskW;
+          const y = (p / maskW) | 0;
+          const light = ((x / tile) | 0) % 2 === ((y / tile) | 0) % 2;
+          d.data[p * 4] = light ? 220 : 180;
+          d.data[p * 4 + 1] = light ? 220 : 180;
+          d.data[p * 4 + 2] = light ? 220 : 180;
+          d.data[p * 4 + 3] = 220;
+        }
+      }
+      octx.putImageData(d, 0, 0);
+      ctx.drawImage(off, 0, 0, canvas.width, canvas.height);
+    }
+    if (bbox && bbox.corners.length === 4) {
+      const c = bbox.corners;
+      ctx.strokeStyle = '#00e5ff';
+      ctx.lineWidth = Math.max(2, canvas.width / 400);
+      ctx.beginPath();
+      ctx.moveTo(c[0][0], c[0][1]);
+      for (let i = 1; i < 4; i++) ctx.lineTo(c[i][0], c[i][1]);
+      ctx.closePath();
+      ctx.stroke();
+      // The axis reads corners[3] → corners[0], the long side.
+      const a = c[3];
+      const b = c[0];
+      ctx.strokeStyle = '#ff3d71';
+      ctx.lineWidth = Math.max(3, canvas.width / 300);
+      ctx.beginPath();
+      ctx.moveTo(a[0], a[1]);
+      ctx.lineTo(b[0], b[1]);
+      ctx.stroke();
+      ctx.fillStyle = '#ff3d71';
+      ctx.beginPath();
+      const ang = Math.atan2(b[1] - a[1], b[0] - a[0]);
+      const r = Math.max(10, canvas.width / 60);
+      ctx.moveTo(b[0], b[1]);
+      ctx.lineTo(b[0] - r * Math.cos(ang - 0.4), b[1] - r * Math.sin(ang - 0.4));
+      ctx.lineTo(b[0] - r * Math.cos(ang + 0.4), b[1] - r * Math.sin(ang + 0.4));
+      ctx.closePath();
+      ctx.fill();
+    }
+  };
+
+  const redraw = async () => {
+    if (!blob || !canvas) return;
+    const gen = ++decodeGen;
+    decoding = true;
+    let bmp: ImageBitmap | null = null;
+    try {
+      bmp = await decodeOrientedBitmap(blob);
+      if (gen !== decodeGen || !canvas) return;
+      imgW = bmp.width;
+      imgH = bmp.height;
       canvas.width = imgW;
       canvas.height = imgH;
       applyFit();
-      ctx.drawImage(img, 0, 0);
-      if (maskBitset && maskW > 0 && maskH > 0) {
-        const off = document.createElement('canvas');
-        off.width = maskW;
-        off.height = maskH;
-        const octx = off.getContext('2d')!;
-        const d = octx.createImageData(maskW, maskH);
-        const tile = 8;
-        for (let p = 0; p < maskW * maskH; p++) {
-          if (!maskBitset[p]) {
-            const x = p % maskW;
-            const y = (p / maskW) | 0;
-            const light = ((x / tile) | 0) % 2 === ((y / tile) | 0) % 2;
-            d.data[p * 4] = light ? 220 : 180;
-            d.data[p * 4 + 1] = light ? 220 : 180;
-            d.data[p * 4 + 2] = light ? 220 : 180;
-            d.data[p * 4 + 3] = 220;
-          }
-        }
-        octx.putImageData(d, 0, 0);
-        ctx.drawImage(off, 0, 0, canvas.width, canvas.height);
-      }
-      if (bbox && bbox.corners.length === 4) {
-        const c = bbox.corners;
-        ctx.strokeStyle = '#00e5ff';
-        ctx.lineWidth = Math.max(2, canvas.width / 400);
-        ctx.beginPath();
-        ctx.moveTo(c[0][0], c[0][1]);
-        for (let i = 1; i < 4; i++) ctx.lineTo(c[i][0], c[i][1]);
-        ctx.closePath();
-        ctx.stroke();
-        // The axis reads corners[3] → corners[0], the long side.
-        const a = c[3];
-        const b = c[0];
-        ctx.strokeStyle = '#ff3d71';
-        ctx.lineWidth = Math.max(3, canvas.width / 300);
-        ctx.beginPath();
-        ctx.moveTo(a[0], a[1]);
-        ctx.lineTo(b[0], b[1]);
-        ctx.stroke();
-        ctx.fillStyle = '#ff3d71';
-        ctx.beginPath();
-        const ang = Math.atan2(b[1] - a[1], b[0] - a[0]);
-        const r = Math.max(10, canvas.width / 60);
-        ctx.moveTo(b[0], b[1]);
-        ctx.lineTo(b[0] - r * Math.cos(ang - 0.4), b[1] - r * Math.sin(ang - 0.4));
-        ctx.lineTo(b[0] - r * Math.cos(ang + 0.4), b[1] - r * Math.sin(ang + 0.4));
-        ctx.closePath();
-        ctx.fill();
-      }
-    };
-    img.src = url;
+      const ctx = canvas.getContext('2d')!;
+      ctx.clearRect(0, 0, canvas.width, canvas.height);
+      ctx.drawImage(bmp, 0, 0);
+      paintOverlays(ctx);
+    } finally {
+      if (bmp) bmp.close();
+      if (gen === decodeGen) decoding = false;
+    }
   };
 
-  $: if (url || bbox || maskBitset) void tick().then(redraw);
+  $: if (blob || bbox || maskBitset) void tick().then(redraw);
 
   onMount(() => {
     if (stage) parentW = stage.clientWidth;
@@ -119,12 +122,12 @@
     return () => ro.disconnect();
   });
   onDestroy(() => {
-    if (url) URL.revokeObjectURL(url);
+    decodeGen += 1;
   });
 </script>
 
 <div class="stage" bind:this={stage}>
-  {#if url}
+  {#if imgW > 0 || decoding || blob}
     <canvas bind:this={canvas}></canvas>
   {:else}
     <div class="loading">Decoding photo…</div>
diff --git a/frontend/src/capture/decodeOrientedBitmap.test.ts b/frontend/src/capture/decodeOrientedBitmap.test.ts
new file mode 100644
index 0000000..df757ae
--- /dev/null
+++ b/frontend/src/capture/decodeOrientedBitmap.test.ts
@@ -0,0 +1,149 @@
+import { test, afterEach } from 'node:test';
+import assert from 'node:assert/strict';
+import { readFileSync } from 'node:fs';
+import { fileURLToPath } from 'node:url';
+import { dirname, join } from 'node:path';
+import {
+  decodeOrientedBitmap,
+  ORIENTED_BITMAP_OPTIONS,
+} from '../decodeOrientedBitmap.ts';
+
+const here = dirname(fileURLToPath(import.meta.url));
+const fixturePath = join(here, '../../tests/fixtures/set1-48x2/face-a.jpeg');
+
+const RealCreateImageBitmap = globalThis.createImageBitmap;
+
+afterEach(() => {
+  if (RealCreateImageBitmap === undefined) {
+    delete (globalThis as unknown as { createImageBitmap?: unknown }).createImageBitmap;
+  } else {
+    globalThis.createImageBitmap = RealCreateImageBitmap;
+  }
+});
+
+/** Minimal EXIF Orientation + largest SOF size for the orient-8 fixture. */
+function readJpegOrientAndSof(buf: Buffer): { orientation: number; sofW: number; sofH: number } {
+  let orientation = 1;
+  const exif = buf.indexOf(Buffer.from('Exif\0\0'));
+  if (exif >= 0) {
+    const tiff = exif + 6;
+    const le = buf[tiff] === 0x49;
+    const u16 = (o: number) => (le ? buf.readUInt16LE(o) : buf.readUInt16BE(o));
+    const u32 = (o: number) => (le ? buf.readUInt32LE(o) : buf.readUInt32BE(o));
+    const ifd = tiff + u32(tiff + 4);
+    const n = u16(ifd);
+    for (let k = 0; k < n; k++) {
+      const e = ifd + 2 + k * 12;
+      const tag = u16(e);
+      const typ = u16(e + 2);
+      if (tag === 0x0112) {
+        orientation = typ === 3 ? u16(e + 8) : u32(e + 8);
+      }
+    }
+  }
+  let sofW = 0;
+  let sofH = 0;
+  let i = 0;
+  while (i < buf.length - 9) {
+    if (buf[i] === 0xff && buf[i + 1] >= 0xc0 && buf[i + 1] <= 0xc3) {
+      const h = buf.readUInt16BE(i + 5);
+      const w = buf.readUInt16BE(i + 7);
+      if (w * h > sofW * sofH) {
+        sofW = w;
+        sofH = h;
+      }
+      const segLen = buf.readUInt16BE(i + 2);
+      i += 2 + segLen;
+    } else {
+      i += 1;
+    }
+  }
+  return { orientation, sofW, sofH };
+}
+
+/** Orientation 5–8 swap width/height for display. */
+function orientedSize(sofW: number, sofH: number, orientation: number): { w: number; h: number } {
+  if (orientation >= 5 && orientation <= 8) return { w: sofH, h: sofW };
+  return { w: sofW, h: sofH };
+}
+
+test('fixture face-a.jpeg is EXIF Orientation 8 (stored landscape → oriented portrait) (#72)', () => {
+  const buf = readFileSync(fixturePath);
+  const { orientation, sofW, sofH } = readJpegOrientAndSof(buf);
+  assert.equal(orientation, 8, 'matched-set JPEGs carry Orientation 8');
+  assert.equal(sofW, 4000);
+  assert.equal(sofH, 2256);
+  const { w, h } = orientedSize(sofW, sofH, orientation);
+  assert.equal(w, 2256);
+  assert.equal(h, 4000);
+});
+
+test('decodeOrientedBitmap always requests imageOrientation from-image (#72)', async () => {
+  let seen: ImageBitmapOptions | undefined;
+  (globalThis as unknown as { createImageBitmap: typeof createImageBitmap }).createImageBitmap =
+    async (_src: ImageBitmapSource, opts?: ImageBitmapOptions) => {
+      seen = opts;
+      return { width: 2256, height: 4000, close() {} } as ImageBitmap;
+    };
+
+  const blob = new Blob([readFileSync(fixturePath)], { type: 'image/jpeg' });
+  const bmp = await decodeOrientedBitmap(blob);
+  assert.deepEqual(seen, ORIENTED_BITMAP_OPTIONS);
+  assert.equal(ORIENTED_BITMAP_OPTIONS.imageOrientation, 'from-image');
+  assert.equal(bmp.width, 2256);
+  assert.equal(bmp.height, 4000);
+});
+
+test('decodeOrientedBitmap falls back to bare createImageBitmap if option rejected (#72)', async () => {
+  let calls = 0;
+  (globalThis as unknown as { createImageBitmap: typeof createImageBitmap }).createImageBitmap =
+    async (_src: ImageBitmapSource, opts?: ImageBitmapOptions) => {
+      calls += 1;
+      if (opts && 'imageOrientation' in opts) {
+        throw new TypeError('imageOrientation unsupported');
+      }
+      return { width: 90, height: 160, close() {} } as ImageBitmap;
+    };
+
+  const bmp = await decodeOrientedBitmap(new Blob([new Uint8Array([1, 2, 3])], { type: 'image/jpeg' }));
+  assert.equal(calls, 2, 'retry bare after option rejection');
+  assert.equal(bmp.width, 90);
+  assert.equal(bmp.height, 160);
+});
+
+test('decodeOrientedBitmap: Chromium orients fixture to 2256×4000 (#72)', async (t) => {
+  let chromium: typeof import('@playwright/test').chromium;
+  try {
+    ({ chromium } = await import('@playwright/test'));
+  } catch {
+    t.skip('playwright not available');
+    return;
+  }
+  const browser = await chromium.launch();
+  try {
+    const page = await browser.newPage();
+    const buf = readFileSync(fixturePath);
+    const b64 = buf.toString('base64');
+    // Inline the same contract as decodeOrientedBitmap (worker-safe, no bundler).
+    const dims = await page.evaluate(async (b64jpeg: string) => {
+      const bin = atob(b64jpeg);
+      const arr = new Uint8Array(bin.length);
+      for (let i = 0; i < bin.length; i++) arr[i] = bin.charCodeAt(i);
+      const blob = new Blob([arr], { type: 'image/jpeg' });
+      const opts = { imageOrientation: 'from-image' as const };
+      let bmp: ImageBitmap;
+      try {
+        bmp = await createImageBitmap(blob, opts);
+      } catch {
+        bmp = await createImageBitmap(blob);
+      }
+      const out = { w: bmp.width, h: bmp.height };
+      bmp.close();
+      return out;
+    }, b64);
+    assert.equal(dims.w, 2256, `oriented width (got ${dims.w})`);
+    assert.equal(dims.h, 4000, `oriented height (got ${dims.h})`);
+  } finally {
+    await browser.close();
+  }
+});
diff --git a/frontend/src/capture/session.ts b/frontend/src/capture/session.ts
index 528d4ad..59e73fa 100644
--- a/frontend/src/capture/session.ts
+++ b/frontend/src/capture/session.ts
@@ -10,6 +10,7 @@ import { measure } from '../measure/measure';
 import { orientedRect } from '../geometry/rect';
 import { encodeInventoryPng, type InventoryInput } from '../png/inventory';
 import { encodeOverlayPng, type EncodeOverlayInput } from '../png/overlay';
+import { decodeOrientedBitmap } from '../decodeOrientedBitmap';
 
 const DEBOUNCE_MS = 2000;
 const BUSY_MS = 300;
@@ -512,7 +513,7 @@ export function createCaptureSession(opts: SessionOpts = {}): CaptureSession {
       if (state.k !== 'measure') return;
       const { source, approvedMask, axis, lengthEighths, thicknessEighths } = state;
       if (lengthEighths === 0 || thicknessEighths === 0) return;
-      const bitmap = await createImageBitmap(source.blob);
+      const bitmap = await decodeOrientedBitmap(source.blob);
       const base = measure(
         approvedMask.bitset, source.widthPx, source.heightPx,
         axis.bbox, lengthEighths, thicknessEighths, approvedMask.slabPx,
@@ -587,7 +588,7 @@ export function createCaptureSession(opts: SessionOpts = {}): CaptureSession {
             widthPx: derived.widthPx,
             heightPx: derived.heightPx,
           };
-          const siblingBitmap = await createImageBitmap(photo.blob);
+          const siblingBitmap = await decodeOrientedBitmap(photo.blob);
           let encoded: { blob: Blob; sourceBelowFloor: boolean };
           try {
             encoded = await encodeInventory({ bitmap: siblingBitmap, mask: derived.mask, source: siblingSource });
diff --git a/frontend/src/decodeOrientedBitmap.ts b/frontend/src/decodeOrientedBitmap.ts
new file mode 100644
index 0000000..07e8928
--- /dev/null
+++ b/frontend/src/decodeOrientedBitmap.ts
@@ -0,0 +1,29 @@
+/**
+ * Shared decode for capture photos so PhotoStage, mask worker, inventory, and
+ * calculate all share one EXIF-oriented pixel space.
+ *
+ * Matched-set / DJI JPEGs often carry EXIF Orientation 8 (stored landscape,
+ * display portrait). `new Image()` and bare `createImageBitmap(blob)` can
+ * disagree across browsers → pink axis arrow space ≠ mask/overlay bitset space.
+ *
+ * Contract: always request `imageOrientation: 'from-image'`. If the runtime
+ * rejects that option (older engines), fall back to bare `createImageBitmap`;
+ * engines that already apply EXIF by default still match Image/canvas size.
+ * Engines that never apply EXIF may still diverge after fallback — document
+ * that path rather than inventing a software rotate.
+ */
+export const ORIENTED_BITMAP_OPTIONS: ImageBitmapOptions = {
+  imageOrientation: 'from-image',
+};
+
+export async function decodeOrientedBitmap(blob: Blob): Promise<ImageBitmap> {
+  try {
+    return await createImageBitmap(blob, ORIENTED_BITMAP_OPTIONS);
+  } catch (first) {
+    try {
+      return await createImageBitmap(blob);
+    } catch {
+      throw first;
+    }
+  }
+}
diff --git a/frontend/src/png/overlay.test.ts b/frontend/src/png/overlay.test.ts
index b9c53f3..37f8656 100644
--- a/frontend/src/png/overlay.test.ts
+++ b/frontend/src/png/overlay.test.ts
@@ -545,6 +545,43 @@ function tiltedAxis25Fixture() {
   return { W, H, bitset, bbox, ux0, uy0, rx0, ry0, halfL, cx, cy };
 }
 
+
+test('buildOverlayPlan: angleDeg=90 vertical long side → width left→right within 2° of horizontal (#72)', () => {
+  // Upright slab: approved length axis is vertical (angleDeg 90). Width marks must
+  // run left→right ≈ horizontal (atan2 ≈ 0 or ±π), not slanted with the photo.
+  const W = 200, H = 400;
+  const bitset = new Uint8Array(W * H);
+  for (let y = 40; y <= 360; y++) {
+    for (let x = 60; x <= 140; x++) bitset[y * W + x] = 1;
+  }
+  const prev = minAreaRect(bitset, W, H)!;
+  const bbox = orientedRect(prev, 90);
+  assert.equal(bbox.angleDeg, 90);
+  const scale = 10; // 320px span ≈ 32"
+  const plan = buildOverlayPlan({
+    bitset,
+    widthPx: W,
+    heightPx: H,
+    bbox,
+    scale,
+    lengthIn: 32,
+    lengthLabel: '32"',
+    mapToInventory: (x, y) => [x, y],
+  });
+  assert.ok(plan.widths.length > 0, 'expected width stations');
+  for (const w of plan.widths) {
+    const ang = Math.atan2(w.right[1] - w.left[1], w.right[0] - w.left[0]);
+    // Fold to [-90, 90] so left→right and right→left both count as horizontal.
+    let deg = (ang * 180) / Math.PI;
+    if (deg > 90) deg -= 180;
+    if (deg < -90) deg += 180;
+    assert.ok(
+      Math.abs(deg) <= 2,
+      `width station ${w.stationIn} left→right must be within 2° of horizontal (atan2 deg=${deg.toFixed(2)}; left=${w.left} right=${w.right})`,
+    );
+  }
+});
+
 test('buildOverlayPlan: length a→b || approved (ux,uy); width left→right || (rx,ry) (#70)', () => {
   const { W, H, bitset, bbox, cx, cy } = tiltedAxis25Fixture();
   const scale = 10;
diff --git a/frontend/src/worker/mask.worker.ts b/frontend/src/worker/mask.worker.ts
index d7caa6c..8844901 100644
--- a/frontend/src/worker/mask.worker.ts
+++ b/frontend/src/worker/mask.worker.ts
@@ -1,5 +1,6 @@
 import { minAreaRect, slabBounds } from '../geometry/rect';
 import type { MaskParams, WorkerIn, WorkerOut } from '../capture/capture.types';
+import { decodeOrientedBitmap } from '../decodeOrientedBitmap';
 
 let bitmap: ImageBitmap | null = null;
 let data: Uint8ClampedArray | null = null;
@@ -69,7 +70,7 @@ self.onmessage = (e: MessageEvent<WorkerIn>) => {
     }
     data = null;
     w = h = 0;
-    createImageBitmap(msg.blob)
+    decodeOrientedBitmap(msg.blob)
       .then((bmp) => {
         w = bmp.width;
         h = bmp.height;