I looked at various reference pictures while painting this illustration. I drew the cats myself, roughly traced the basic outlines of the girl from a photograph, and picked a palette of 10 colors from the same photograph. I did not paint this image onto the photograph though, I looked at it from another monitor during painting. Photo is taken by another friend of ours. Additionally, I searched "yawn cat" at www.gettyimages.com, and looked at various cat photos that pop up while painting the cats in the illustration. It's a personal portfolio piece. Hope you like it...

Here is a link to the original photograph:
http://www.jefftreves.com/Uykucular/Uykucu.jpg

Here is a link to "making of Sleepyheads" as an animated GIF:
http://www.jefftreves.com/Uykucular/Uykucu-MakingOf.gif