I've made my living as a graphic designer for over thirty years. Photoshop is my specialty.
Lavinia, if you have Photoshop, you can use the blend features to overlap photos and get all kinds of cool effects. The brush and artistic filters are fun to play with, too. The fake cover I made for Mystic Taxi is just a simple overlap, but I used a feathered eraser to get rid of the male character's maroon background. The taxi is an authentic photo of the first taxi cab. I softened the edges, then made it a sepia toned duotone, and used the "overlay" blending feature to give it a ghostly look. The photo of the buildings is from a NYC architectural website. It's conveys a perfect tone for the story. It was fun to make and took me about 15 minutes.