You can do it pretty easily with Automator (comes with OS X) http://www.peachpit.com/blogs/blog.aspx?uk=Mac-Productivity-Quick-Scripts-and-Workflows--Set-Deskt

You can do it pretty easily with Automator (comes with OS X) http://www.peachpit.com/blogs/blog.aspx?uk=Mac-Productivity-Quick-Scripts-and-Workflows--Set-Desktop-to-Astronomy-Picture-of-the-Day http://www.peachpit.com/blogs/blog.aspx?uk=Mac-Productivity-... I'd recommend changing it to "Get URLs of images linked from these webpages" though, to get the high-res version.