The designs are created by individual artists that have stores on Zazzle.com. Zazzle is a print on demand company with a wide variety of designs to choose from. Most designs can also be personalized with your special message, wedding date, bride's and groom's names, etc.
The postage stamps are peel and stick, making them easy to apply to your invitations. You can choose from mostly ocean, mostly sand, and some with hints of other beachy things.