This is one of Magnus' toys. Get the source of this script (SVN: browse/use). New: Next-generation toys!
 Bug reports and feature requests

CatLitter

A tool to mass-add categories and templates to images. Images in "Category:Media needing categories" are grouped by user, as users tend to upload similar files.
Analyzing "Category:Media needing categories". This might take a few seconds...
0 distinct users have uploaded files to "Category:Media needing categories".
Selecting 20 users at random...
Using 0 images from category "Media needing categories"