Click on the screen size you are using. To find out what screen resolution you are using, hit: Start>Settings>Control Panel. Then double click the Display icon. Under the Settings tab, there should be a slider at the bottom right corner that say screen area. Make a note of what this says. It's most likely one of the three sizes we have listed here.
Right click on image once it loads
Choose "Set as Wallpaper" That should be it for Windoes 98+.
For earlier operating systems, under Start/Settings/Control Panel, open Display
This won't work for earlier version of MacOS: Only desktop patterns can be displayed. Displaying a full picture requires software programs such as Deskpicture or Decor.