I'm a big fan of ffffound.com's image bookmarking site. Here's a local, client-side version of that service let's you archive images for offline viewing. It works by adding a "Save this image" item to your browser's context menu. Selecting the menu item while clicking on an image saves the binary image data and its context (the page url, date, etc) in browser storage. You can then view your saved images by pointing your browser at localhost:8080/archiver?offset=0.

More information available at lilyapp.org