How to run a photography contest to get good photographs to use in website?

Does anybody know how to run a photography contest as a way to get good photographs to use in your website?

We are a start-up just building our website and are considering whether to run a photography contest to help us find a good photograph for the home page of our website.

Does anybody have any experience of running a photography contest in order to achieve a similar goal?

And if so, what is a cost effective, successful and easy way to run such a contest?

All advice and suggestions will be well received.