I look for pictures on google images with "Creative Commons" licensing. Then I just layer any text I want on top of it using an online text editor.
Any person can pics a copyrighted picture, and then publish it as "creative commons". Be careful. Not all photos on google are tagged in the right way.
To the OP: why don't you just use what you're feeling like using? or take your own pictures, and use them? And I don't get why you wanna use Rick Ross' image on a "this is a Rick Ross type of beat" song you uploaded. People won't like it more just because you've put a photo of him there, you know?
If you aren't selling the music does it really matter? Most pictures are posted by many people all over the internet. Just curious, Does it really matter if its just for fun?
I know, but it give the listener the impression. It make it look even cooler. Adds more low end to your mix and make it sound better.