Thread:Project:Support desk/Auto watermark on upload/reply

No pre-bundled extension. However MediaWiki will (when used with image magick) add a file comment including the url from where it was retrieved from. This is viewable in most image metadata viewers including MediaWiki. (As an example, see the file comment field of this image from commons )

You can also use $wgCustomConvertCommand to use a custom argument to ImageMagick to make it add a watermark. See image magick docs for details on how to do that.

(As an aside, using metadata for source information instead of watermarks is nice since it doesn't alter physical appearence of image, which can detract from the beauty of some images depending on what type of image it is).