Thread:Project:Support desk/Are there any possible way to add watermark to mediawiki's image system?/reply

Note mediawiki already adds invisible metadata saying things like File source: http://commons.wikimedia.org/wiki/File:%25_of_U.S._households_connected_by_age.png, which is readable by programs like exiftool. (This is only on the thumbnails. MediaWiki doesn't touch the original image).

You can also use $wgCustomConvertCommand in order to set a custom command for making thumbnails, which can be used to add a visible watermark.