nice write up.. just today I asked for a service that would do this http://news.ycombinator.com/item?id=1514991 ( sorry for thread hijack) but basically I didn't want to do image processing on the same instance as the app is running because of the constraints of cloud instances.

Based on your steps listed here 1.Handle request 2.Fetch original source image from S3 3.Resize/apply effects 4. Return result back to user. Why not just resize/apply at time of upload and store in S3... are you resizing and applying effects on every request for an image ?