DISCLAIMER: I had no idea where to put this question, so I apologize if it is in the wrong forum. I would appreciate if a mentor could correct its placement if necessary. [mentor's note: moved to computers & technology as this best fits the software aspect of this question] So, I have been working on a little book for physics self-studiers with a 9th grade mathematics background to learn moderately advanced physics. I know it will probably never go anywhere, but it is nevertheless a fun project. So, my question is, where should I go to get high-quality figures for free and without legal issues if it is ever published or posted online. If I would have to make them to avoid legal issues, what should I use to do that. Thanks!