I posted this in a different thread related to the Genre image but it applies for the Artist image as well. I'm hoping this bug is fixed so you can either choose your own image or not have the same image displayed twice.
"It appears Poweramp is selecting the genre image by looking at the first song (in alphabetical order) from "All Songs" that contain that specific genre tag. This would be ok if each song only had 1 genre tag. Unfortunately I have up to 7 genres tagged on thousands of songs, so one song in particular displays as the album cover for genres Chillout, Downtempo, Experimental, Instrumental, Nu Jazz, and Trip Hop. It would be nice if Poweramp would not use the same album cover twice when it displays genre covers. Is this a feature that will soon be available?"