Can I include frames from anime and/or fanart in my game?

So I have a bit of a strange question. I'm making my first game and I want to make a little Easter egg to thank the people that have helped me. I decided that having an image for each person in a hard to reach location would be good.

As my question states, one of my friends has asked if I can include a character from his favorite anime. I expect another to ask for a specific piece of fanart of a character as well. I understand the fanart would probably be easily determined by asking the artist if they are okay with it, but what about the anime? To be clear, he simply snipped a frame of the anime where his favorite character was and sent it to me.