Programe a smart picture service website

a simple website that needs to serve as a picture distributor for our clients. we like to upload all our pictures in high format and then the system create different download sized versions for our cli8enst to download. we also have a corporation with a service that makes white bag ground as well as transparent pictures which we want to integrate to on this system. We open this system for others as a paid service for them us use same service, in a way that the can easily change colours and font and upload their own logo. Payment is be monthly and by amount of traffic used. we need the system to be managed on a cms like wordpress or other system the design part is very simple and is pretty much done, we need only some adjustment to the design that's all. rest is system development.