Lamb Chopper by Larry Houghton

The easiest way to use a picture as wallpaper in Windows is to simply use the "set as wallpaper" option in your browser.

Choose and click the resolution you want (it should match your screen resolution if possible).
The picture will appear at the resolution you have chosen. Wait for it to finish loading.
Right-click on the picture. A menu will appear. From that menu, choose "set as wallpaper." That's all there is to it.