When studying commercial art one thing that the teachers impress upon you is to create a reference library and to only use your own reference material in your work, if at all possible.
So it has carried over, forty something years later. In this instance, I shoot the crow and I shoot the moon (not at the same time.)
Have I purloined other people's images in the past and not given them credit?
I have but I try no to. Better to use your own work. Thank you Jim Hulbert.