Seriously, in terms of Art, I think it's okay if someone created the image from scratch, even though it was inspired by so-n-so. However, the artist sould at least show props to their inspirers.
If I painted the Mona Lisa, from scratch. Total knock off of Michelangelo work, I can, by right, sell the painting for whatever amount I choose. If someone love the image, it doesn't matter where it came from. The original artist will have a difficult time to contest anything in court because, although the work is strikingly similar, the work that was put behind it was done by someone else.
The fuzzy part about this whole issue, is claiming of ownership. Sure, I can say that I painted the Mona Lisa, but if I said I came up with it, would make people think I was insane. Why? Popularity, of course! It's a sad reality, because if so-n-so took the monkey image from a youtube tutorial, (which youtubers should read the terms and conditions carefully btw) and someone did an exact monkey image only altering it a little, we'll that is really difficult to gage who did what when. On the other side of the coin, what if the person that posted the tutorial, took the idea from the Monkey in the Galaxy image and made a vid about it. How would one know who did what when? If someone could prove that they had their image licensed first, is usually the winner. :(