CompuServe described GIF, and then Gershon Elber and I made an open-source implementation that became ubiquitous
Worth noting that multiple years span the time between when Elber actually wrote giflib and when ESR added 2 functions and 3 utilities to it.
http://esr.ibiblio.org/?p=1404#comment-242133
http://esr.ibiblio.org/?p=1404#comment-242156
Bottom line: libgif and libpng.