Click an image to view the larger size. Then select the button under the one you want to send.
Im sure most people realise how these work. You appeal to the sentimentality or emotional impact. Gather some images that people to your site will be interested in, they in turn send an image to a friend, who HAS to come to your site to collect it, while they are they, they may look around, or they may pick a card to send to another friend. Either way, you get more visitors