rethumb is a image processing HTTP API, we accept image transformation or information requests, cached them and send the response as fast as possible.
Lets check an example to see how things work.
Start with an image that you want to process: http://images.rethumb.com/image_coimbra_600x600.jpg
By accessing our API you will be able to create thumbnails:
On the first time we will download the original image, process it and save the result. When someone access the API URL for the second time the response is already cached and ready to go. All our API works in this way and the kept the responses (thumbnails or json information) for a minimum of six months.
We also have paid plans that give you access to paid features: http://rethumb.com/pricing.
Out tutorials also explain how to use rethumb in different programming languages: http://rethumb.com/tutorials.