[robski]

I have to agree with Duncan.

Imagine you took a photo of an innocent man looking suspicious in the street getting into his car. His features fully recognisable. At a later date you sell the image for a Police Poster which indicates the guy is trying to steal the car. Unless the guy signed an agreement to let it be used for this purpose you could be up to your neck in libel suits.

Release forms can also be used to prevent a professional model (who was paid to sit for the session) claiming a share of the profits should the photo find its way onto a household item.