From the idea of Juan Xavier of websnapr  I started yesterday to write my own screenshot capture engine, and it is working already very nice. I registered a new domain called thumboo  (thumbnails and a cool "oo" as it is in Google or whatever).
With thumboo you are able to create several screenshots. There are four different thumbnails starting at 92x70 pixel. The screenshot is captured at 1024x768 pixel and resized to the smaller version. One screenshot is done at a screen size of 1024x768 pixel, but you will loose the bottom of the web page. For this reason I have added one more screenshot that will show the full page, see these examples below.
I will add more features like screenshot history and subscriptions to configure the interval screenshots should be taken. I hope this service will be interesting for anyone who is building web sites.