diff --git a/README.md b/README.md
index 68e0fdf..89329c2 100644
--- a/README.md
+++ b/README.md
@@ -34,6 +34,12 @@ If you only need to regenerate thumbnails, run:
 npm run build:thumbs
 ```
 
+To force a full thumbnail rebuild, run:
+
+```sh
+npm run build:thumbs:force
+```
+
 ## Image Conventions
 
 - Full-size images and thumbnails share the same numeric ID
@@ -45,6 +51,7 @@ npm run build:thumbs
 ## Thumbnail Focus
 
 Thumbnails are generated from `images/fulls` with `sharp` at `240x320`.
+The generator auto-rotates images using EXIF orientation, skips unchanged files by default, and removes stale thumbnail `.jpg` files that no longer map to a meal entry.
 
 For images that should crop away from the center, add optional thumbnail focus metadata to the meal entry:
 
diff --git a/images/thumbs/.thumbs-manifest.json b/images/thumbs/.thumbs-manifest.json
new file mode 100644
index 0000000..e68a568
--- /dev/null
+++ b/images/thumbs/.thumbs-manifest.json
@@ -0,0 +1,308 @@
+{
+  "meal:01": {
+    "version": 1,
+    "width": 240,
+    "height": 320,
+    "quality": 82,
+    "mtimeMs": 1770500129000,
+    "size": 1052830,
+    "focus": {
+      "x": 0.35,
+      "y": 0.5
+    }
+  },
+  "meal:02": {
+    "version": 1,
+    "width": 240,
+    "height": 320,
+    "quality": 82,
+    "mtimeMs": 1770500128000,
+    "size": 835360,
+    "focus": null
+  },
+  "meal:03": {
+    "version": 1,
+    "width": 240,
+    "height": 320,
+    "quality": 82,
+    "mtimeMs": 1770500128000,
+    "size": 1034158,
+    "focus": {
+      "x": 0.5,
+      "y": 0.35
+    }
+  },
+  "meal:04": {
+    "version": 1,
+    "width": 240,
+    "height": 320,
+    "quality": 82,
+    "mtimeMs": 1770500128000,
+    "size": 1090215,
+    "focus": null
+  },
+  "meal:05": {
+    "version": 1,
+    "width": 240,
+    "height": 320,
+    "quality": 82,
+    "mtimeMs": 1770500128000,
+    "size": 1122236,
+    "focus": {
+      "x": 0.5,
+      "y": 0.35
+    }
+  },
+  "meal:06": {
+    "version": 1,
+    "width": 240,
+    "height": 320,
+    "quality": 82,
+    "mtimeMs": 1770444049000,
+    "size": 676787,
+    "focus": null
+  },
+  "meal:07": {
+    "version": 1,
+    "width": 240,
+    "height": 320,
+    "quality": 82,
+    "mtimeMs": 1770500128000,
+    "size": 872024,
+    "focus": null
+  },
+  "meal:08": {
+    "version": 1,
+    "width": 240,
+    "height": 320,
+    "quality": 82,
+    "mtimeMs": 1770500128000,
+    "size": 618276,
+    "focus": null
+  },
+  "meal:09": {
+    "version": 1,
+    "width": 240,
+    "height": 320,
+    "quality": 82,
+    "mtimeMs": 1770500127000,
+    "size": 1349804,
+    "focus": null
+  },
+  "meal:10": {
+    "version": 1,
+    "width": 240,
+    "height": 320,
+    "quality": 82,
+    "mtimeMs": 1770500128000,
+    "size": 1071870,
+    "focus": null
+  },
+  "meal:11": {
+    "version": 1,
+    "width": 240,
+    "height": 320,
+    "quality": 82,
+    "mtimeMs": 1770500128000,
+    "size": 764329,
+    "focus": null
+  },
+  "meal:12": {
+    "version": 1,
+    "width": 240,
+    "height": 320,
+    "quality": 82,
+    "mtimeMs": 1770500128000,
+    "size": 1172905,
+    "focus": null
+  },
+  "meal:13": {
+    "version": 1,
+    "width": 240,
+    "height": 320,
+    "quality": 82,
+    "mtimeMs": 1770500129000,
+    "size": 1099540,
+    "focus": null
+  },
+  "meal:14": {
+    "version": 1,
+    "width": 240,
+    "height": 320,
+    "quality": 82,
+    "mtimeMs": 1770500128000,
+    "size": 1052362,
+    "focus": null
+  },
+  "meal:15": {
+    "version": 1,
+    "width": 240,
+    "height": 320,
+    "quality": 82,
+    "mtimeMs": 1770500128000,
+    "size": 1227608,
+    "focus": null
+  },
+  "meal:16": {
+    "version": 1,
+    "width": 240,
+    "height": 320,
+    "quality": 82,
+    "mtimeMs": 1770500127000,
+    "size": 840466,
+    "focus": null
+  },
+  "meal:17": {
+    "version": 1,
+    "width": 240,
+    "height": 320,
+    "quality": 82,
+    "mtimeMs": 1770500128000,
+    "size": 1136990,
+    "focus": null
+  },
+  "meal:18": {
+    "version": 1,
+    "width": 240,
+    "height": 320,
+    "quality": 82,
+    "mtimeMs": 1770500127000,
+    "size": 1261294,
+    "focus": null
+  },
+  "meal:19": {
+    "version": 1,
+    "width": 240,
+    "height": 320,
+    "quality": 82,
+    "mtimeMs": 1770500128000,
+    "size": 1119498,
+    "focus": null
+  },
+  "meal:20": {
+    "version": 1,
+    "width": 240,
+    "height": 320,
+    "quality": 82,
+    "mtimeMs": 1770500128000,
+    "size": 868085,
+    "focus": null
+  },
+  "meal:21": {
+    "version": 1,
+    "width": 240,
+    "height": 320,
+    "quality": 82,
+    "mtimeMs": 1770500128000,
+    "size": 1057896,
+    "focus": null
+  },
+  "meal:22": {
+    "version": 1,
+    "width": 240,
+    "height": 320,
+    "quality": 82,
+    "mtimeMs": 1770500128000,
+    "size": 1088795,
+    "focus": null
+  },
+  "meal:23": {
+    "version": 1,
+    "width": 240,
+    "height": 320,
+    "quality": 82,
+    "mtimeMs": 1770500129000,
+    "size": 852307,
+    "focus": null
+  },
+  "meal:24": {
+    "version": 1,
+    "width": 240,
+    "height": 320,
+    "quality": 82,
+    "mtimeMs": 1770500129000,
+    "size": 1149955,
+    "focus": null
+  },
+  "meal:25": {
+    "version": 1,
+    "width": 240,
+    "height": 320,
+    "quality": 82,
+    "mtimeMs": 1770500129000,
+    "size": 1242099,
+    "focus": null
+  },
+  "meal:26": {
+    "version": 1,
+    "width": 240,
+    "height": 320,
+    "quality": 82,
+    "mtimeMs": 1770500128000,
+    "size": 1414024,
+    "focus": null
+  },
+  "meal:27": {
+    "version": 1,
+    "width": 240,
+    "height": 320,
+    "quality": 82,
+    "mtimeMs": 1770500128000,
+    "size": 1022877,
+    "focus": null
+  },
+  "meal:28": {
+    "version": 1,
+    "width": 240,
+    "height": 320,
+    "quality": 82,
+    "mtimeMs": 1770500129000,
+    "size": 1018868,
+    "focus": null
+  },
+  "meal:29": {
+    "version": 1,
+    "width": 240,
+    "height": 320,
+    "quality": 82,
+    "mtimeMs": 1770500128000,
+    "size": 1233602,
+    "focus": null
+  },
+  "meal:30": {
+    "version": 1,
+    "width": 240,
+    "height": 320,
+    "quality": 82,
+    "mtimeMs": 1770500129000,
+    "size": 739786,
+    "focus": null
+  },
+  "meal:31": {
+    "version": 1,
+    "width": 240,
+    "height": 320,
+    "quality": 82,
+    "mtimeMs": 1771126436000,
+    "size": 1069693,
+    "focus": null
+  },
+  "meal:32": {
+    "version": 1,
+    "width": 240,
+    "height": 320,
+    "quality": 82,
+    "mtimeMs": 1771226059000,
+    "size": 995282,
+    "focus": null
+  },
+  "meal:33": {
+    "version": 1,
+    "width": 240,
+    "height": 320,
+    "quality": 82,
+    "mtimeMs": 1771226144000,
+    "size": 729224,
+    "focus": null
+  }
+}
diff --git a/package.json b/package.json
index c32cc86..7b9e0ac 100644
--- a/package.json
+++ b/package.json
@@ -4,7 +4,8 @@
   "scripts": {
     "build": "npm run build:thumbs && npm run build:pages",
     "build:pages": "node scripts/build.js",
-    "build:thumbs": "node scripts/generate-thumbnails.js"
+    "build:thumbs": "node scripts/generate-thumbnails.js",
+    "build:thumbs:force": "node scripts/generate-thumbnails.js --force"
   },
   "dependencies": {
     "sharp": "^0.34.5"
diff --git a/scripts/generate-thumbnails.js b/scripts/generate-thumbnails.js
index d1ceff1..efb539b 100644
--- a/scripts/generate-thumbnails.js
+++ b/scripts/generate-thumbnails.js
@@ -6,7 +6,9 @@ const { loadMeals, repoRoot } = require("./lib/meals");
 
 const fullsDir = path.join(repoRoot, "images", "fulls");
 const thumbsDir = path.join(repoRoot, "images", "thumbs");
+const manifestPath = path.join(thumbsDir, ".thumbs-manifest.json");
 
+const THUMB_VERSION = 1;
 const THUMB_WIDTH = 240;
 const THUMB_HEIGHT = 320;
 const JPEG_QUALITY = 82;
@@ -15,6 +17,16 @@ function clamp(value, min, max) {
   return Math.min(Math.max(value, min), max);
 }
 
+function parseArgs(argv) {
+  return {
+    force: argv.includes("--force"),
+  };
+}
+
+function getManifestKey(mealId) {
+  return `meal:${mealId}`;
+}
+
 function getThumbnailPaths(meal) {
   return {
     fullPath: path.join(fullsDir, `${meal.id}.jpg`),
@@ -22,6 +34,24 @@ function getThumbnailPaths(meal) {
   };
 }
 
+function getOrientedDimensions(metadata) {
+  if (!metadata.width || !metadata.height) {
+    throw new Error("Could not determine image dimensions");
+  }
+
+  if ([5, 6, 7, 8].includes(metadata.orientation)) {
+    return {
+      width: metadata.height,
+      height: metadata.width,
+    };
+  }
+
+  return {
+    width: metadata.width,
+    height: metadata.height,
+  };
+}
+
 function getCropArea(width, height, focus) {
   const targetRatio = THUMB_WIDTH / THUMB_HEIGHT;
   const sourceRatio = width / height;
@@ -48,43 +78,137 @@ function getCropArea(width, height, focus) {
   };
 }
 
-async function generateThumbnail(meal) {
+function loadManifest() {
+  if (!fs.existsSync(manifestPath)) {
+    return {};
+  }
+
+  return JSON.parse(fs.readFileSync(manifestPath, "utf8"));
+}
+
+function getThumbSignature(meal, sourceStats) {
+  return {
+    version: THUMB_VERSION,
+    width: THUMB_WIDTH,
+    height: THUMB_HEIGHT,
+    quality: JPEG_QUALITY,
+    mtimeMs: sourceStats.mtimeMs,
+    size: sourceStats.size,
+    focus: meal.thumbnail?.focus ?? null,
+  };
+}
+
+function manifestEntryMatches(currentEntry, nextEntry) {
+  return JSON.stringify(currentEntry) === JSON.stringify(nextEntry);
+}
+
+async function removeStaleThumbnails(expectedIds) {
+  if (!fs.existsSync(thumbsDir)) {
+    return 0;
+  }
+
+  const entries = await fs.promises.readdir(thumbsDir, { withFileTypes: true });
+  let removed = 0;
+
+  for (const entry of entries) {
+    if (!entry.isFile() || path.extname(entry.name).toLowerCase() !== ".jpg") {
+      continue;
+    }
+
+    const id = path.basename(entry.name, path.extname(entry.name));
+
+    if (expectedIds.has(id)) {
+      continue;
+    }
+
+    await fs.promises.unlink(path.join(thumbsDir, entry.name));
+    removed += 1;
+  }
+
+  return removed;
+}
+
+async function generateThumbnail(meal, manifest, options) {
   const { fullPath, thumbPath } = getThumbnailPaths(meal);
 
   if (!fs.existsSync(fullPath)) {
     throw new Error(`Missing full-size image for meal ${meal.id}: ${fullPath}`);
   }
 
-  const image = sharp(fullPath);
-  const metadata = await image.metadata();
+  const sourceStats = await fs.promises.stat(fullPath);
+  const signature = getThumbSignature(meal, sourceStats);
+  const thumbExists = fs.existsSync(thumbPath);
 
-  if (!metadata.width || !metadata.height) {
-    throw new Error(`Could not read image dimensions for ${fullPath}`);
+  if (
+    !options.force &&
+    thumbExists &&
+    manifestEntryMatches(manifest[getManifestKey(meal.id)], signature)
+  ) {
+    return {
+      mealId: meal.id,
+      changed: false,
+      manifestEntry: signature,
+    };
   }
 
-  const cropArea = getCropArea(
-    metadata.width,
-    metadata.height,
-    meal.thumbnail?.focus
-  );
+  const image = sharp(fullPath);
+  const metadata = await image.metadata();
+  const { width, height } = getOrientedDimensions(metadata);
+
+  const cropArea = getCropArea(width, height, meal.thumbnail?.focus);
 
   await image
+    .rotate()
     .extract(cropArea)
     .resize(THUMB_WIDTH, THUMB_HEIGHT)
     .jpeg({ quality: JPEG_QUALITY, mozjpeg: true })
     .toFile(thumbPath);
+
+  return {
+    mealId: meal.id,
+    changed: true,
+    manifestEntry: signature,
+  };
+}
+
+function writeManifest(manifest) {
+  const sortedEntries = Object.entries(manifest).sort(([left], [right]) =>
+    left.localeCompare(right, undefined, { numeric: true })
+  );
+
+  const orderedManifest = Object.fromEntries(sortedEntries);
+  fs.writeFileSync(manifestPath, `${JSON.stringify(orderedManifest, null, 2)}\n`);
 }
 
 async function main() {
+  const options = parseArgs(process.argv.slice(2));
   const meals = loadMeals();
+  const manifest = loadManifest();
+  const nextManifest = {};
+  const expectedIds = new Set(meals.map((meal) => meal.id));
 
   await fs.promises.mkdir(thumbsDir, { recursive: true });
 
+  const removed = await removeStaleThumbnails(expectedIds);
+  let generated = 0;
+  let skipped = 0;
+
   for (const meal of meals) {
-    await generateThumbnail(meal);
+    const result = await generateThumbnail(meal, manifest, options);
+    nextManifest[getManifestKey(meal.id)] = result.manifestEntry;
+
+    if (result.changed) {
+      generated += 1;
+    } else {
+      skipped += 1;
+    }
   }
 
-  console.log(`Generated ${meals.length} thumbnails in images/thumbs`);
+  writeManifest(nextManifest);
+
+  console.log(
+    `Thumbnail build complete: ${generated} generated, ${skipped} skipped, ${removed} removed`
+  );
 }
 
 main().catch((error) => {
diff --git a/scripts/lib/meals.js b/scripts/lib/meals.js
index 00151ce..22e7303 100644
--- a/scripts/lib/meals.js
+++ b/scripts/lib/meals.js
@@ -47,6 +47,8 @@ function validateMeals(meals) {
     throw new Error("data/meals.json must contain an array");
   }
 
+  const ids = new Set();
+
   for (const [index, meal] of meals.entries()) {
     if (!meal || typeof meal !== "object") {
       throw new Error(`Meal at index ${index} must be an object`);
@@ -62,6 +64,12 @@ function validateMeals(meals) {
       throw new Error(`Meal ${index} has a non-string "position" value`);
     }
 
+    if (ids.has(meal.id)) {
+      throw new Error(`Duplicate meal id "${meal.id}" found in data/meals.json`);
+    }
+
+    ids.add(meal.id);
+
     validateThumbnail(meal, index);
   }
 }