Website to allow users to place images on top of an existing image

I want to create a website where users can upload an photo, then select from a number of additional images and position one or more of them on top of the uploaded image. The user must then be able to save the finished image to their computer, probably as a JPG. To clarify with an example - users will be models who wish to censor their images to make them acceptable for MySpace and Facebook (these websites ban you for uploading images containing nudity). So, models will upload a topless photo and position one image over each breast to censor it, etc. In addition to being positioned on top of the uploaded image, the additional images must also be resizable. There is no need for logins or user profiles - the website will be open to everyone. I want to keep it simple. When the user has completed their image, they will click "OK" and will then be prompted to save the finished image to their computer. If you want more information, or if you have any questions, please contact me.