You use Zoom Out from the Windows menu to reduce the photo or a selected portion of the photo by a factor of two (to a minimum of 1:16). You can also use the Command key and the minus key (ΓÇô) from the numeric keypad to zoom out on a photo.
Alternatively, you can use the Command key and the Option key to zoom out on a photo. Position the mouse cursor on the photo to select the area you want to zoom. Hold down both the Command key and the Option key. The cursor changes to a magnifying glass containing the minus symbol (ΓÇô). Click the mouse to zoom out on the photo.