You have a Website, but the content belongs to other people? Does this mean that you are acting like a photo host? Do you have established contracts with these other content providers? If not, then using anyone else's work could be a copyright violation, worse if you are doing so prominently. Exceptions can be made, but if you've redistributed someone's work that came from someone else's camera, the general answer is to stop what you're doing and get an agreement from the photographer before proceeding further.
Saying things like "Credit: Some Guy at www.whatever" doesn't grant you the right to redistribute someone's work. My gallery is very hard about that, and I had to strip several old images out because I didn't have an explicit agreement in verbal or written form. Implied consent from a family member was not enough for the third-party images to be accepted, even if the person used my camera and I did the processing. The person has to say or write something that can be interpreted as a transfer of copyright ownership, or the image doesn't get accepted.
You really cross into a trouble zone if "use" means commercial use. Be careful about what commercial use means. It doesn't mean selling prints or otherwise making money for personal or business profit, for which you could be sued for any money made from the sale of someone else's work. Commercial use occurs when you use an image to endorse or otherwise advertise a product, which could include your own business or a corporate product. Misuse of an image during an act of commercial use is a debilitating lawsuit waiting to happen. Such a lawsuit can cover both money earned and your legal liability for misuse, to include misrepresentation of a person or a prominent building for which the art in the architecture is protected by copyright or trademark.
I suggest reviewing the copyright laws governing your particular situation, and consult with a competent attorney if you are confused about any potential disputes between yourself and your clients. What you're suggesting sounds illegal and not worth the trouble. Make your own photographs or buy a commercial license for stock photography for your own uses.