To add a Backdrop to your mailing you should click the “Backdrop” button in the menu that appears to the left of your card design on the Customize page. The Backdrop menu will appear on the left and you can browse different images (all Backdrops cost 1 coin per recipient.)
You can remove the backdrop by clicking the “Remove Backdrop” button below the menu:
Please note that Backdrops will not appear in the email your recipients receive. They will only appear on the website once your recipients click to view their card.