If a person is using your pictures for a diferent person the solution may be to add the name and parents to a line at the bottom of the picture before you post it.

It is easy to add text to pictures with many image viewers like Irfanview. If they still take the picture an attach it erroneously to their tree, it will demonstrate the quality of their research to have a picture of x daughter of y and z, and the picture identifies the person a N daughter of O an P.