https://unicornify.pictures (see also https://news.ycombinator.com/item?id=24281401 )

If you want bigger and/or higher-quality images, the avatar generation code (including a command-line app) is at https://bitbucket.org/balpha/go-unicornify.

The code appears to have been migrated to GitHub at https://github.com/codingisacopingstrategy/unicornify and the about page on https://web.archive.org/web/20100428132341/http://unicornify...

The code is also at https://bitbucket-archive.softwareheritage.org/projects/ba/b...