For Windows users: Right click on the image, and a menu will appear. Choose "set as background" or "set as wallpaper".
Mac users: Move your cursor over the image, hold your mouse button down until
you see a menu and select "Save This Image As." In the dialog box that pops up,
choose where you'd like to save the image. Go inside your apple menu to control
panel, and select "appearance". In appearance, select Desktop, then click "place
picture." Select the image file you saved and click "choose." Select "position
automatically." Click "set desktop" and close the window.