Set Mac OS X Desktop Background Wallpaper from any Image in Safari
You can set any image as your Mac OS X desktops background wallpaper directly from Safari, all you need to do is right-click on the image and select “Use Image as Desktop Picture”. The default setting appears to be ‘Fill Screen’ so if you select an image smaller than your screen resolution it might not look that great.
In terms of web browsers, this feature seems to be limited only to Safari, as Chrome and Firefox don’t include the option. However, you can also right-click on any image within the Finder and set your background image there too.