This is something that I worried about for a long time. While making games, it is hard to tell for sure if any of the resources are copyrighted unless a person is clearly aware that they are to a like to an image that have known in certain work done. I wanted to make a 2D MMO, that in certain ways might be similar to "Pokémon". I did not want to make an illegal game, but it is just that there are certain elements that I want in the game which are similar to those in "Pokémon". I also wanted to possibly sell the features of it, if the project succeeds and works out all well. What exactly are some ways that I can find out for sure if images that I am using are illegal to use or not.
The element which I am worried about in the game which I was planning to make was about creature battling and summoning. Thankfully, game concepts cannot be copyrighted, but I did not want to take or use images that were exactly like those in "Pokémon", and I wanted to make a game that is very different in many ways. I might have wanted to use creatures in a similar cartoon fashion that is used in "Pokémon". This has been somewhat of a concern, to me, though as about the legal issues possibly.