Website screenshots and thumbnails
Website thumbnails are resized pictures of web pages. It's possible to automate this with Linux tools such as gnome-web-photo. You might need a full dedicated server for this stuff. A cheap VPS cannot manage this as you'll end up spending time wondering why xserver doesn't start up.
You need a dedicated server or, of course, you can use your own server for this purpose. Don't think that a cheap VPS or some other form of hosting service could be sufficient!
A complete page is first fetched and then rendered (or this may happen in parallel as well). This actually takes quite a bit of juice from your server if there are tens of concurrent operations taking place. In addition, the bandwidth should be sufficient for this purpose as well.
Common problems are Linux xserver, fake requests, recursion, the Webkit itself etc. At worst, your server becomes slow making it hardly possible to login via ssh! Some sort of flow control is also needed as you cannot serve an arbitrary number of requests at the same time. What happens is that the server starts to swap and appears awfully slow.