# Image Watermarking

## Objective

Stamp a logo or text mark onto images before they leave the app.

An automatic overlay of a logo or text mark applied to images at the point they are served, downloaded, or shared.

## Before You Begin

This feature is being added to an application that already exists and already
works. Do not scaffold a new project, and do not assume a blank slate.

Inspect the codebase first and establish:

- The existing application structure and where code of this kind already lives.
- The framework and version in use.
- The existing design system — colours, spacing, typography, and component conventions.
- Existing UI components you can reuse instead of writing new ones.
- The existing database structure, if this feature needs to persist anything.
- The existing authentication and authorization system, if this feature is user-scoped.
- Dependencies already installed, so you don't add a library that duplicates one.
- The existing test setup and conventions.

Only start writing code once you understand the above. If the application
already implements part of this feature, extend it rather than replacing it.

## Implementation Instructions

1. Apply the mark when the image is delivered, not when it is uploaded, and cache the marked variant. Burning the mark into the stored file at upload means changing the logo requires reprocessing every asset ever uploaded.
2. Always keep the unmarked original, and serve it to the owner and to anyone with an explicit right to the clean file. Reuse the app's existing secure download path to decide who that is.
3. Size and position the mark as a proportion of the image rather than in fixed pixels, so it reads the same on a small thumbnail and on a large photograph.
4. Decide explicitly what happens to the original metadata: strip location and camera data on public delivery, or preserve it, but make it a stated choice rather than whatever the encoder happens to do.
5. Do not treat this as copy protection. A watermark deters casual reuse and nothing more, so do not build access rules that assume the marked image cannot be cropped or edited.

## UI and UX Requirements

Match the application's existing design system exactly. Reuse its components,
spacing, and typography. This feature should look like it was always there.

## Responsive Requirements

Works on mobile, tablet, and desktop. Touch targets are large enough to hit on a
phone, and nothing overflows horizontally at 320px.

## Accessibility Requirements

- Fully keyboard navigable.
- Correct semantic elements and ARIA roles.
- Visible focus states.
- Meets WCAG AA contrast.
- Dynamic changes are announced to screen readers.
- Respects prefers-reduced-motion.

## Edge Cases

- A mark sized in fixed pixels dominates a thumbnail and disappears on a large photo. Scale it as a percentage of the shorter edge and set a floor so it stays legible.
- The owner must always be able to retrieve the clean file. Store the original untouched and gate access to it through the app's existing per-file permission checks.
- A dark mark vanishes on a dark photo and a light one vanishes on a bright sky. Sample the region under the mark and choose a treatment, or add a subtle shadow or outline so it survives both.
- Applying the mark on upload freezes it forever. Generate marked variants on delivery and cache them, and invalidate that cache whenever the mark, its position, or its opacity changes.
- Uploaded photos carry location, device, and timestamp metadata that should usually not be published. Decide deliberately whether the delivered variant strips or preserves it, and apply the same rule everywhere.
- Generating a marked variant on the first request adds latency to that request. Serve a placeholder or the pending state rather than a broken image, and warm the common sizes.
- The mark must not obscure the subject of every image by default. Offer a position choice and a default that sits in a corner with a margin.
- Marked variants must respect the same access rules as the original. A public marked URL must not become a way to enumerate private assets.

## Testing

Exercise the feature end to end in the running application. Cover every edge case
above, then run the existing test suite and confirm nothing regressed.

## Acceptance Criteria

- [ ] Marks are applied on delivery and cached, not burned into the stored original.
- [ ] Changing the mark or its settings invalidates cached variants without reprocessing originals.
- [ ] The unmarked original is retained and reachable only by permitted users.
- [ ] The mark scales proportionally and stays legible across image sizes and brightness.
- [ ] Metadata handling on delivered variants is an explicit, consistent decision.
- [ ] Marked variants enforce the same access rules as the source file.
- [ ] The feature matches the existing design system.
- [ ] No existing functionality is broken.

## Adaptation Rules

- Match the existing design system. Do not introduce a new colour palette,
  spacing scale, or component library.
- Reuse existing components and utilities wherever they fit.
- Follow the naming, file layout, and code style already present.
- Do not upgrade, replace, or remove existing dependencies to make this
  feature fit. Adapt the feature to the app, not the app to the feature.
- Do not break existing functionality. If a change is genuinely required in
  existing code, make the smallest one that works and say so.
- If something in these instructions conflicts with how the application is
  built, follow the application and explain the deviation.

## Final Verification

Before you report the work as done:

1. Re-read the acceptance criteria above and check each one against what you
   actually built.
2. Run the application and exercise the feature end to end.
3. Run the existing test suite and confirm you have broken nothing.
4. Check the feature on mobile, tablet, and desktop widths.
5. Check keyboard navigation and focus handling.
6. Summarize what changed: files added, files modified, and anything you
   deliberately did differently because of how this application is built.

If any acceptance criterion is unmet, fix it before reporting completion.