Easythumb is an alternative to the complete Webthumb API. It has a smaller featureset but only requires a single GET request and supports caching thumbnails on Webthumb's servers.
Easythumb has 2 rates, for non-cached thumbnails the charge is 1 credit. For cached thumbnails the rate is .05 credits per delivery.
The security hash is an md5 hash encoded in hexidecimal containing the following concatenated together
Any example request looks like:
Easythumb requests return an image and include the Content-type headers so they can be used directly in an img tag