What's with the Lion?
It was drawn by the well-known commercial artist Duane Bibby. He used this lion in the illustrations for Donald Knuth's original TeXbook, for Leslie Lamport's LaTeX book, and for other books having to do with TeX, so his work is familiar to everyone in the community. Because of that, his beautiful and insightful drawings have also graced conference posters, tee shirts, and coffee mugs.
You can use this drawing if you like, either personally as on a login screen or publicly as on a web page. For public uses we would appreciate an acknowledgment such as “CTAN lion drawing by Duane Bibby”. You can get high resolution versions in case you want to touch up the scans.
Thank you, Duane!
In the mean time a vectorized version of the drawing in SVG format is available. It increasingly replaces the pixel images on the CTAN portal.