Imagine creating a web app and not having to implement any image scaling. A young version of ScaleDown has been released. It allows scaling images (on the local file system) via a url. So <img src="/images/big.png/400x300/URLHAMC"/> would return an image fitting into a 400x300 rect. There is an HMAC signature, based on url, to prevent unauthorized scaling.

Since this just uses URLs, you could use scale down in your PHP, Python, Javascript, etc, application. Your app just needs to have a HMAC library. Plans are to add distributed capability to allow scaling remote images.