If you've found an image online you'd like as your desktop background, you can follow these instructions to set your background.
Microsoft Internet Explorer (Windows)
|Right click the image and select "Set as Background"|
Apple Safari (Windows and OS X)
|Right click (OS X users can hold Control and click), then select "Use Image as Desktop Picture"|
Mozilla Firefox (Windows and OS X)
|Right click on a picture file and select "Set as Desktop Background"|
|(Windows Users) Select if you want to stretch the picture to fit or not, and optionally choose a desktop background color. Click "Set Desktop Background"|