I'll take you through a sample project in this tutorial'"a mini-mashup if you will'"that will take a photograph, break it up and present it to the user as simple puzzle.

They use a picture from Flickr, the drag & drop feature of the Yahoo UI Library, and some PHP 5 (including GD) to create a simple, fun little application. It shows how to integrate content from one location, use functionality from another, and combine them into one seamless application.