May I use other people's art on my own videos?

Just like Nicetryian, where he has champions displayed before the montage, like the Kha'Zix montage he did, he displays Kha'Zix.

More info: I'm doing a project in school, and I'm going to edit a League of Legends montage, I want it to be perfect, I know the basics, and when im done in 2 weeks, the teacher will look at it, and another teacher will check that it doesn't violate any copyright laws.

So, what I would like to do, is to showcase a picture, maybe fan art, of the main champion that the clip is about, so for example, I made a sick play as Rakan, and would like to showcase Rakan a few seconds before the montage starts.

So, how do I do this without breaking the rules of copyright? I will of course make an intro and outro too that shows all creds.

EDIT: If any other (possibly) human here has some nice art I can include, feel free to share it here, this will also help other new content creators, and maybe inspire people to create more content.

EDIT 2: Might make some minor changes on the video, take away things that is not necessary in a youtube video, after I'm done I might upload it to youtube and will share the result for those who are interested.