Can I use or incorporate pre-existing images in my cover art, merch, or social media, or clips in my music videos?

For the most part, you must obtain permission from the owner of the original artwork (typically, the artist, creator or photographer of the original artwork) if you would like to use it in your work!

Any time you are using all or part of another creator’s work - including images in cover art or images or clips in your music videos - you must make sure that you either have permission from the original creators for your intended purpose, or that the work is not protected by copyright or is truly in the public domain. Derivative images may still be violating the rights of the original copyright owner. 

If you have a license such as from a stock photo or art website, you should confirm that it covers the use you intend to make (e.g. commercial sales of merch). 

You should also separately confirm whether there are any identifiable persons included in the photo/artwork and whether you have permission to use their likeness.