BLIMSHOT is an extension for users of App.net to easily create and share links as 'visual bookmarks' using screenshots of almost any web page.
After installing the extension, you will see the icon to launch it on the right of browser url bar. Clicking it will 'dim' the page you are on. You can then select a rectangle of a page to use as the associated image with a shared link to that page. When you have added or edited any text to go with the post to App.net, it will upload the image to bli.ms and finally send the post to App.net.
A demo screencast can be seen here : http://www.youtube.com/watch?v=UhV525iEatY