For the more famous novels even if the books themselves don't have pictures, you can often find fanart of the characters and locations on the internet that might help you get a better handle on things.

Or find one that has a film/tv adaptation, watch that first and then read the book. I did this with the Power of One movie/book when I was a kid. Hated the book at first, but after seeing the film I went back and it was a totally different (and far superior) experience.