# Batch Watermark Studio

> Add a text or logo watermark to up to 30 images at once: position, tiling, opacity and angle. Stamps a text watermark (choice of installed fonts, size, colour, opacity, angle) or your logo (PNG with transparency, scale, opacity) onto one image or a ZIP of up to 30 images, in a corner, the centre or tiled across the whole picture. Download all results as one ZIP and check the preview of the first image.

Part of usefulweb.site (https://usefulweb.site/). Results are deterministic calculations from the inputs and the listed assumptions; the API returns exactly what the web page shows.

## Use it
- Human interface: https://batchwatermarkstudio.usefulweb.site/ (interactive tool at https://batchwatermarkstudio.usefulweb.site/tool)
- JSON API: POST https://batchwatermarkstudio.usefulweb.site/api/v1/calculate with a JSON object of inputs (schema: https://batchwatermarkstudio.usefulweb.site/api/v1/tool)
- OpenAPI: https://batchwatermarkstudio.usefulweb.site/openapi.json
- MCP (Streamable HTTP): https://batchwatermarkstudio.usefulweb.site/mcp - tool `batch_watermark_studio`

## Inputs
- images (file, required): Image or ZIP of images - One image or a ZIP with up to 30 images (JPG, PNG, WebP, AVIF, GIF, TIFF, HEIC), max 50 MB each and 150 MB in total.
- mode (select): Watermark type
- text (text): Watermark text - For text watermarks. Line breaks are replaced by spaces.
- font (select): Font
- size (number): Size - Text: letter height as % of the shorter image side. Logo: logo width as % of the image width.
- color (text): Text colour - Hex colour, e.g. #ffffff (white) or #000000 (black).
- opacity (integer): Opacity
- angle (integer): Angle - Rotation of the watermark; e.g. -30 for a diagonal tile pattern.
- position (select): Position
- margin (number): Margin - Distance from the edge as % of the shorter side (ignored for centre and tiling).
- logo (file): Logo (for logo watermarks) - PNG or WebP with a transparent background works best, max 10 MB.
- format (select): Output format
- quality (integer): Quality - For JPG, WebP and AVIF.

## Method
- Text is rendered by ImageMagick (label:) with a TrueType font installed on the server, in the chosen colour with the opacity applied to the colour's alpha channel, then rotated. The text is escaped so it is always drawn literally.
- Logos are decoded from their content (PNG, WebP, JPG, GIF, AVIF), scaled to the given share of each image's width, their alpha channel multiplied by the opacity, then rotated.
- Each image is first turned upright from its EXIF orientation. The watermark is composited ("over") at the chosen position with a margin relative to the shorter side, or repeated as a tile pattern with gaps of 6% of the shorter side around each copy.
- Sizes are relative to each image, so mixed resolutions get proportionally equal watermarks. Metadata is removed from the outputs; the ZIP uses fixed timestamps.

## Limits
- Visible watermarks deter casual copying but can be cropped or retouched away.