Download Instructions:
PC: Click the image link relative to your desktop size, then right-click on the enlarged image and select "Set as Wallpaper".
Mac: Click the image link relative to your desktop size, then click and drag the image to your desktop. Next, from the Apple menu, select "Control Panel," then select "Appearance". Finally, select "Desktop," then select "Add Picture," and select the image you just dragged to your desktop, click "Set Desktop".

To determine desktop size:
PC: Right-click on background of current desktop, select "Properties," select "Settings" tab, see "Screen Resolution" for desktop size (e.g., 1280 x 1024 pixels).
Mac: From the Apple menu select "Control Panel," select "Monitors," see "Resolution" for desktop size (e.g., 1280 x 1024, 85Hz).