I was playing around with changing the background image on my new N810, and I eventually figured something out that may be non-obvious to other noobs (or maybe I'm just dumb). To get a right-click menu in the web-browser, tap with the stylus and hold it down for a few seconds. The right-click menu will pop up, and there's an "Image" sub-menu in there with a "Save As..." option. Maybe one of these days I'll take a look at the manual.