diff --git a/scripts/dither-badge-photos.mjs b/scripts/dither-badge-photos.mjs
new file mode 100644
index 0000000..a062b1e
--- /dev/null
+++ b/scripts/dither-badge-photos.mjs
@@ -0,0 +1,98 @@
+#!/usr/bin/env node
+/**
+ * One-shot patch: dither visitor photos before they go on the badge canvas.
+ *
+ *   node scripts/dither-badge-photos.mjs          # patch
+ *   node scripts/dither-badge-photos.mjs --check  # report only
+ *
+ * A thermal head has no grey. Drawn straight, a photo gets thresholded by the
+ * plane conversion and most of a face lands on one side of that threshold, so
+ * it prints as a solid black mass. This inserts a Floyd-Steinberg pass at
+ * exactly the size the photo will occupy.
+ *
+ * Idempotent, writes printer.js.bak, refuses to run if the anchor is missing.
+ */
+
+import fs from 'node:fs';
+import path from 'node:path';
+import { fileURLToPath } from 'node:url';
+
+const here = path.dirname(fileURLToPath(import.meta.url));
+const target = path.resolve(here, '..', 'src', 'printer.js');
+const checkOnly = process.argv.includes('--check');
+
+function fail(message) {
+  console.error(`\n  FAILED: ${message}\n`);
+  console.error('  Nothing was changed.\n');
+  process.exit(1);
+}
+
+if (!fs.existsSync(target)) fail(`${target} does not exist. Run this from the repo root.`);
+
+let source = fs.readFileSync(target, 'utf8');
+const original = source;
+
+if (source.includes('ditherPhoto(')) {
+  console.log('\n  Already patched — printer.js dithers photos. Nothing to do.\n');
+  process.exit(0);
+}
+
+const changes = [];
+
+/* -- 1. Import ---------------------------------------------------- */
+
+const importAnchor = "import { photoAbsolutePath } from './photos.js';";
+if (!source.includes(importAnchor)) fail('could not find the photos.js import');
+
+source = source.replace(
+  importAnchor,
+  `${importAnchor}\nimport { ditherPhoto } from './printing/dither.js';`
+);
+changes.push('added the ditherPhoto import');
+
+/* -- 2. Dither once, at final size, before either draw site ------- */
+
+// Matches the existing line regardless of the exact multipliers, so tweaking
+// the photo size later doesn't break this patch.
+const sizeAnchor = /const photoSize = photo \? Math\.round\([^;]+\) : 0;/;
+const match = source.match(sizeAnchor);
+if (!match) fail('could not find the photoSize calculation in drawBadge');
+
+const insertion = `${match[0]}
+
+  // Thermal heads print pure black or nothing, so a photo has to be reduced to
+  // 1-bit before it lands on the canvas — otherwise the plane conversion
+  // thresholds it into a solid blob. Done once here rather than at each draw
+  // site, and at exactly photoSize: rescaling a dithered image resamples the
+  // dot pattern back into greys and undoes the whole thing.
+  //
+  // Skipped on the measuring pass, which never paints.
+  if (photo && photoSize > 0 && startY !== null) {
+    photo = ditherPhoto(photo, photoSize);
+  }`;
+
+source = source.replace(sizeAnchor, insertion);
+changes.push('drawBadge dithers the photo at its final size');
+
+/* -- 3. Sanity check ---------------------------------------------- */
+
+if (!/let photo = null;/.test(source)) {
+  fail('photo is not declared with let — it cannot be reassigned. Patch by hand.');
+}
+
+console.log('\n  Changes to src/printer.js:');
+for (const c of changes) console.log(`    - ${c}`);
+
+if (checkOnly) {
+  console.log('\n  --check given, nothing written.\n');
+  process.exit(0);
+}
+
+if (source === original) fail('nothing actually changed');
+
+fs.writeFileSync(`${target}.bak`, original);
+fs.writeFileSync(target, source);
+
+console.log(`\n  Wrote ${target}`);
+console.log(`  Backup at ${target}.bak`);
+console.log('\n  Next: docker compose build && docker compose up -d\n');