from their site:
What is Polyvore?
Polyvore is a free, easy-to-use web-based application for mixing and matching images from anywhere on the web. It is also a vibrant community of creative and stylish people.
Polyvore lets you create sets composed of individual images using an easy to use, drag and drop editor. After you have created a set, you can publish and share it with your friends and the Polyvore community.
Try it – it’s easy and fun!