One of the factors that allowed me to learn cartooning was the fact that I would copy anything Disney. I copied all kinds of Disney characters. I drew Disney princesses, Duckburg Ducks, Dopey, Lady and the Tramp, Goofy, Mickey, and Tinkerbell. This is not complete list. Now, I know copying is plagiarism. I know I will never make these characters my own. But Disney taught me to draw. I picked up on many Disney techniques. Walt Kelly eyes… rubber hose arms… child-faces… cartoon animals… eagles… Well, here’s a sample of my bald-faced thievery of Disney ideas.
Catch a Falling Star 
if copying a painting is plagiarism then all great artists were once plagiarists who later added a bit or two to the stolen objects and after that ofcourse moved on.
painting is not writing where you can imagine things, in painting we need models, so we can draw the outlines 🙂
I have to admit, I am not serious when I accuse myself of plagiarism. I taught myself to draw by copying from artists I admire; Norman Rockwell, Maxfield Parrish, Salvador Dali, Walt Kelly, Charles Shultz, Dr. Seuss. I still have tons of artwork that are copied from these sources. But I try hard never to claim those as my own work. Like you brought out, you start with those basic images and add, mangle, vivisect, and re-combine to make the art which is your own.