Pexels is always quite good for these kind of things. Bookmark it up for the future! https://www.pexels.com/search/fire/
Post the finished product when you're done, would be great to see how you've got along!
I think it depends where you are in the world, but a lot of copyright law is regulated internationally - for instance the Berne Convention now covers the majority of countries in the world and has standardised much of the law. If you are concerned with someone else using an image, what you might...
My basic understanding of copyright law is that if you do work for someone else, then it is legally theirs unless they give you permission to use it - see the case of Donahue v Allied Newspapers. The best bet would be to not use anything until they've given you permission to use...
As I'm sure you can gather from my username, I'm completely new to Photoshop. Live in England and thought this could be a good way to expand my photography hobby!
Looking forward to learning as much as possible