Prostock-
anything in the public arena where people have 'no reasonable expectation of privacy' can be photographed.
the rule is: "If I can see it, I can shoot it." (think Brittany and Lindsey and Paris)
Geico does not get a cut when I sell an image of them, although I GIVE them prints and posters because I like em and I hope one day they will give me a ride in the Platinum.
selling a print of a photo does not automatically grant additional rights to said image, although that can be part of the deal.
rights to an image can vary depending on the needs of the customer-
such as digital use only, one-time use, limited use, unlimited use, etc
all spelled out in a contract.