I do not wish to open up a can of worms on this, but I have my reservations on the subject of copyright, and how it it justifiably works. In the case of photographs, the duration of the copyright is 25 years from the 1st January of the year the photo was taken.
However, the Copyright Law does state that owners of such things as photographs whether private or commercial should register the said photos which then are recorded, and the photo is replaced with a Copyright copy, and the original returned to the owner and/or stored in the Data base.
If photos are not registered to the copyright office, then it is highly unlikely that if a photo was used, the owner would have the evidence to prove the use of the photo. It would be your word against theirs. Unlikely to stand up in court without registration.
Dont worry, I am not going to flood the forum with illicit photos, but it is worth knowing as a forum owner/administrator you will unlikely surrcome to any problems with copyright rulings.