Here is an example of low level versus mid level paintings. The first painting is a confidant painting done around level 5, the third is a confidant panting done around level 2. My Sim will always be able paint that sleeping kitten now, but will never paint that lion again. Same with the romantic one on the right. After a certain point, they are 'too talented' to paint stick figures any more.
http://i1371.photobucket.com/albums/ag300/Liz_Amsden/11-18-14_4-26nbspPM_zpse67d4809.png
I suppose we could work on making a list here on the forums. I could post all of the common painting that my Sims has done, and see if there are any that people know about that are missed, and just go through the different categories.