Browshot's simple API makes it very easy to request screenshot and retrieve a thumbnail in a single URL.
Take a look at the simple API section to understand how to generate the URL.
no credit card required
Browshot is a web service to create real time web screenshots in a multitude of virtual devices, including mobile devices like the iPhone 3 & 4, iPad, Android Nexus, etc.
Real time screenshots
15+ mobile devices: iPhone, iPad, Android, etc.
30+ desktop resolutions
Fast and reliable
Thumbnails of any size, any ratio
Full API, open-source libraries