I've been surprised at how many folks have asked me for a copy of a release to have these photos used on the Internet. Every time you go to have your picture taken, you should get such a release. You never know when you might want that picture on the net. If you're in the business of setting up Senior Pics, it's a good idea to get the photographer to sign a general such release before signing the contract - and then give the students a photocopy. Sure, there are instances of joint authorship.
Models are a great example.
A joint effort, where clear authorship on both sides is intended. To have the right to make, and derive all profits from, the reprints, enlargements, etc. We don't choose formal photographers because they make lousy pictures. They are entitled to the fruits of their expertise. The protection is less, but nonetheless there.