Image Watermark | Add Text or Logo Locally

The browser checks the file signature instead of trusting only the extension or declared MIME type. It accepts static PNG, JPEG, and WebP data and rejects APNG or animated WebP before rendering so an animation cannot be reduced silently to one frame.

Source safeguards apply to compressed bytes and decoded size: at most 20 files, 10 MiB and 16,384 pixels per side per source, 40,000,000 pixels per source, and 100,000,000 pixels across the batch. Logo images have separate 2 MiB, 8,192-pixel-side, and 16,000,000-pixel limits.

Text watermarks support up to 200 Unicode code points, a 10-200 pixel font size, hexadecimal color, 1-100% opacity, and -180 to 180 degree rotation. Logo scale is based on the target canvas rather than the logo's raw pixel dimensions.

Each selected position is calculated from the rotated watermark bounds. When the requested text or logo would extend beyond the image, the renderer can scale it down to keep the complete mark inside the canvas padding.

Rendering creates new pixels and then encodes PNG as PNG, JPEG as JPEG, and WebP as static WebP. JPEG and WebP encoding can change file size or introduce compression differences, while PNG output can remain lossless but may be larger.

The new raster does not copy source EXIF, GPS, IPTC, or XMP metadata. This is useful for sharing copies but is not a substitute for a forensic metadata audit, and a watermark itself does not prevent copying, cropping, screenshots, or removal.