Just a few nuggets of legal information:
1. Giving credit to someone is not a legal defence for using the works in an unauthorised manner. Credit is just but one factor in which copyright holders decide whether or not to grant the license.
So long as a license to use is not granted, giving credit is as useless and will be regarded as infringement.
Up till this day, I have no idea why the "internet generation" thinks that they can copy/cut/paste just as long as they give credit. That is a seriously wrong and major legal misconception.
2. It is not a legal defence against infringement for the modelling agency to say "the model gave me, I don't know". The fact is that copyright is infringed by reproduction of the work on your website, irrespective of who gave you the photos.
If the model is not authorised to grant you a sub-license to use the work, then you are prima facie, infringing the work.
3. If a photographer owns copyright in the work and gives photos to the model for fun, grattitude, etc, it does not matter that no terms were said. It does not mean that if a copyright holder gave a license to use without stating explicitly what it CANNOT be used for, the licensee (ie model) can use it in any way he/she wants.
All the copyright holder needs to do is inform the model "From today, such use is prohibited", thereby modifying the scope of the initial license granted. So long as the scope of the initial license is not granted irrevocably, the copyright holder always retains the right to modify the license any way he wants.
If he feels sufficiently pissed off, the copyright holder/photographer, can even revoke all past licenses granted and tell the model "too bad, since you pissed me off, I am now revoking my license granted previously and you now CANNOT use it anywhere - if you do, such use is infringing".
I hope this helps to clarify the strong legal position of photographers who own copyright in their works and for those who think they can easily exploit this, to really think twice before proceeding.