Example swappification. Click to open if it isn’t animating for you.
Its purpose is to let you specify two images. The Swapper will load your two images and display the first one for you. When you move your mouse cursor over the first image, the second image will appear. When you move your mouse cursor away from the second image, the first image will appear. This gives you a way to quickly flip between two images to compare them. Give it a try! There are some sample images there to get you started.