I have a website where visitors can upload photos to the site. Yesterday CNN contacted me because they wanted to use some of the photos on their site. I don't have any type of user agreement that covers photo usage. Do the photos that my visitors upload become my property once they post them on the site?
Even if your members are seemingly savvy businesses or organizations, it's been my experience that you can't trust them regarding photo rights. Very often I've had a chamber of commerce submit a professional photo that they claimed was theirs only to find that they had just purchased rights for a print brochure. Your electronic and print distribution rights now need to be spelled out in a written release from the original owner when you accept the content. Professional photographers now patrol the web routinely using image search and/or tips from friends.
The minute something is fixed in tangible form the creator author of it (in this case the photographer) legally owns all rights to it.
Copyright ownership cannot be legally tranferred to you by someone simply uploading a photo to your web site it has to be in writing.
What you may want to do is make sure those uploading the photos to your site legally own them and have the right to publish and distribute them. If they don't then you can be held liable for illegal distribution of copyrighted content.