Do I need a model release form if I use a picture of my granddaughter on the cover of my book? I’m the one who took the photograph.
Yes, you must obtain a model release form. If the child is a minor, you must obtain a form from her parent or court-appointed legal guardian. If she is an adult, you must obtain a form from her directly. Some people assume all authors and publishers are rich, and will sue for anything they can think of. Even if you get along with your granddaughter (or her parent/guardian) now, you may not forever. Your granddaughter could someday marry some jerk who forces her to sue you for a share of the profits of your book because she was used on the cover with no contract in place. Heck, her kids could sue you someday on her behalf if they take control over her affairs for any reason. Never, ever assume that things will always be rosy, especially where family is concerned. Money can make otherwise sensible people do really greedy and stupid things.
When is doubt, always, ALWAYS get it in writing.
You can find a sample model release form here: