Have you seen those websites which display your website thumbnail images beside your sites listing. Many of these websites import these images from Alexa.
You too can now display Alexa Thumbnail Images of Web sites on your websites easily. The Alexa Site Thumbnail web service provides developers with access to thumbnail images for the home pages of web sites and enables developers to enhance web sites, search results, web directories, blog entries, and other web real estate with Alexa thumbnail images.
It is no longer free and you will be charged $0.0002 / thumbnail returned (i.e. $0.20 per 1,000 thumbnails). Pay only for what you use and there is no charge if the thumbnail does not exist.
All thumbnail images are accessible via web services, using SOAP or REST. Developers need to download the Alexa Site Thumbnail Utility Package, in your language of choice to get started. Read the Getting Started and Developer guides to implement Alexa thumbnails on your site.
[Updated Dec 2006 to reflect new policy change]