Flutterby™! : Photo Credits

I have a question that I thought I'd be able to answer on Photo.net - but I can't figure out the semantics for the search... I am putting together a cookbook. Almost all of the photographs in the book were taken by my mother-in-law specifically for the cookbook. That is, she setup a place with good lighting, arranged the photo and took the picture, with only one purpose in mind: the cookbook. Her name is going on the front of the book as "Photography by ..."

However, we have about a half-dozen or so images taken by myself and others. These I thought I would credit on the copyright page. There is one picture of my wife and I that was taken with my camera by an anonymous bystander. How do I credit this photo?

References to discussions on other forums would be helpful. Educated guesses, less-so.