Right mouse click on the image and select "Set as Background"
|Wallpaper for MAC OS9:
Control-click and select "Save this Image as" or "Download image
to Disk" to your desktop.
Go to Apple menu > Control Panel and select "Appearance".
Select the "Desktop" tab and select the "Place Picture.." button.
Locate the image on your desktop.
Click "Set Desktop" or drag the image into the "Current Desktop
|Wallpaper for MAC OS X:
Control-click and select "Download image to Disk".
Save image to desktop.
Go to Apple menu > System Preferences > Personal section and select "Desktop".