PLAIN PhotoPOSTOS, clean and classic.
Available in popular 4x6 and larger 5x7 inch sizes.
Use as is or create clever Mail Art too. Samples below.

Use Plain as is or create Mail Art. Here’s a quick and easy Valentine. To prevent embellishments from snagging as your Mail Art masterpiece travels through the postal system, choosing embellishments with smooth edges and corners are recommended.

Remember that your finished postcard was originally two separate pieces...a PhotoPOSTOS and your photo, and so creating clever Mail Art can be an interesting challenge and have the recipient of your postcard wondering how you created it.
To make a similar Mail Art to the one above or to make a special Valentine’s card: Die-cut a shape into a PhotoPOSTOS postcard. Cut out a small piece of patterned or decorative, lightweight paper to a shape and size that is slightly larger than the cut out. Peel off part of the PhotoPOSTOS back liner that immediately surrounds the cut out shape to expose a little bit of the adhesive. Position the decorative paper behind the opening. This exposed adhesive will help keep the paper in place while you are moving to the next step of adhering your photo to the PhotoPOSTOS. When your photo and PhotoPOSTOS are finally adhered together, this piece of paper will be sandwiched between the two and show through. To create star trails, short pieces of yellow, thin twine were slipped into the opening before finally adhering the photo and PhotoPOSTOS together.
Variation on this theme: Instead of cutting a shape out of a PhotoPOSTOS postcard, cut a shape out of your photo, and follow same instructions.
Embellish with eyelets, or brads BEFORE you stick your photo and PhotoPOSTOS together. Once again embellishments with smooth edges and corners will reduce the chances of these items snagging as your Mail Art masterpiece goes through the postal system. For an added touch these eyelets were filled with glitter glue.

Emboss your message and add a few eyelets to create an effect and enhance your message.