Re: I don't understand all the ramifications, but...
"Unless it is a picture of a model, in which case the model retains copyright unless a waiver is signed."
Nope, the photographer always retains copyright on the work they created, unless it is explicitly given, sold or licensed to someone(s) else. It's the *usage* of the photo that's the issue. Very generally speaking, model releases are usually required (depending on jurisdiction) if there is intended or potential future "commercial" use of the images by one or both parties. They may also act to limit usage (e.g. for 'portfolio' or 'promotion' use only, etc), or if certain private or otherwise copyrighted works may be in the image in a private capacity. The model never owns copyright unless explicitly given by the photographer in an agreement (which could be in the release, if agreed). As an aside: model releases are not needed (generally speaking) for images used for editorial and/or news purposes, or for general pictures taken in public places - although good manners should ideally play a part in those, but we can dream...