Since Alexa stopped offering their free thumbnail service last year a lot of thumbnail services are available now. Some of them offering limited free services and others only a paid premium version. On of the bigger and better services is Girafa, a thumbnail service with a free service and also premium services for users with more then 2000 image requests a month.

He includes the simple code needed to make the request (inside of a thumbnail() function) and shows an example of how to fetch and store the resulting image.