Comment on Valentine's day by Anna-Marine

It isn't hard to say where you have to cut the line.  The line is cut when the original resource is identifiable.  All artists use reference, and when they do most of them go out of their way to either make sure it looks different from the original in every way, or make sure to credit the original.

Regardless, the artist here should stop selling this as a print and put up a link to Apple.  An apology might be warranted as well.