Developer Reference

API Documentation

Integrate bulk watermarking into your pipeline. No account required during beta.

Quick Start

Watermark an image with a single API call:

cURL

curl -X POST https://astamp.io/api/watermark \
  -F "image=@photo.jpg" \
  -F "text=© 2026 My Brand" \
  -F "opacity=0.5" \
  -F "position=bottom-right" \
  -o watermarked.jpg

Authentication

Not required during beta

The API is open during beta. Rate limits are enforced per-IP. API key authentication will be available when accounts launch.

POST

/api/watermark

Apply a watermark to one or more images. Returns the watermarked file(s).

Parameter	Type	Required	Description
image	File	Yes	Image file (PNG, JPEG, WebP, TIFF)
text	String	No*	Watermark text. Required if no logo.
logo	File	No*	Logo image file. Required if no text.
opacity	Float	No	0.0–1.0. Default: 0.5
position	String	No	top-left, center, bottom-right, tiled. Default: bottom-right
rotation	Integer	No	Degrees. Default: 0
format	String	No	Output format: png, jpeg, webp. Default: source format

POST

/api/preview

Generate a low-res preview of the watermark applied to a single image. Same parameters as /api/watermark, returns a 480px-wide preview.

Rate Limits

Anonymous (Beta)

10 req/min

Authenticated (Coming)

100 req/min

Rate limit headers (X-RateLimit-Remaining) are included in every response.

Errors

Code	Meaning
400	Bad request — missing or invalid parameters
413	File too large (max 20 MB per image)
415	Unsupported media type
422	Image rejected (bomb protection or format mismatch)
429	Rate limit exceeded
500	Internal server error