I encountered a problem with a picture, where I didn't know if I needed a model release form or not. I had the picture in my database, and I had to use it only as an accessory, a small part of the total picture.
The people from AOP explained to me that it can be used, because you can only see a mole from her body, which is not a reference to recognize a person. If there were tattoos, or the face could be seen, then I would have needed a model release form.
However, to be sure and not have problems, I chose to cartoonize the picture, so that the picture is as unrecognizable as possible.