Yes, but the OP is not talking about some random adult.
It's her child, who she is raising. There's lots of things you wouldn't force an adult to do - that argument doesn't really apply. If an adult came over and trashed my house, I wouldn't make them clean it up, I just wouldn't invite them over again. I'm raising my kids, though, so I need to teach them how to behave.
I think the OP sounds like she's on top of the situation and handling it beautifully, but for the sake of the larger argument I want to say this.
This doesn't sound so much like it's an issue of having oneself photographed, but of teaching children that they are part of a family and, as such, have some obligations that might occasionally make them uncomfortable. I want my children to learn this. I want them to know that even though they think their great-grandparents are kind of scary-looking, they still have an obligation to act as politely as they can as is appropriate for their age/development. It's kind of the same, I think.
Well said. I completely agree!
And teenagers do need to be forced to do things sometimes!!!!!