It's a nice tutorial, but why wasting the time to do all this if everything you need to download images is your browser's cache? There is FF addon called CacheViewer that let's you conveniently browser your cache, preview the files and save them directly to your preferred folder. I often used it to download banner from sponsors if they don't offer a zip file and it saves me from downloading each banner separately.

The only work I can see some sense in, is protecting against hotlinking, but all the other stuff really won't do the trick unless there is a way of keeping the browser's cache out of the game.