SmugMug sells 4x8 flat cards on photographic paper as well as 5x7 folded cards on cardstock. To turn a photo into a card-ready image, you can use SmugMug's handy create a card feature, which is pre-loaded with lots of templates.
Or, you can make a card-ready image yourself in a program like Photoshop, add that image to your SmugMug site, and order cards from it. A regular photo is NOT card-ready. It must meet our specifications to print correctly.
Here are some examples of card-ready images:

Vertical 4x8 flat card

Horizontal 4x8 flat card

Horizontal 5x7 folded card

Vertical 5x7 folded card
Here's how to make your own from scratch:
1. Create a file in a program like photoshop that is the proper dimensions:
4x8 horizontal: 1200 pixels high, 2400 pixels wide
4x8 vertical: 2400 pixels high, 1200 pixels wide
5x7 horizontal: 4000 pixels wide, 2800 pixels high
5x7 vertical: 2800 pixels high, 4000 pixels wide
2. Keep in mind that you don't want to put any critical content (like text) close to an "edge"
The lab will trim a bit of the image away when the card is processed, so design your card to include a cushion between the content and the edge. Also, on 5x7 folded cards, the lower left corner on the backside of the card will have a barcode printed so that is not a good spot for a critical design element. If you're making a 4x8 photo card, skip to step 4.
3. For a 5x7 folded card, figure out which quartile of your image corresponds with which side of the printed card.
The lab will slice your image in half, and print both sides of a long strip of cardstock. Finally, the cardstock is folded in half to make the finished card. This visual may help:

After determining your "cut" line and fold lines, you can proceed to design your card and add photos, text and other content. Design elements can traverse a fold, but you'll want to avoid putting someone's face on the fold, for instance. Each 5x7 side of the card will be 2000x2800 on the finished product.
4. Save your card as a jpeg and add it to your SmugMug site like you would any other image.
5. Add it to your shopping cart and purchase cards.
Keep in mind that only you, as the logged-in account owner will be able to purchase cards from your account. If you are a pro, you cannot yet set a custom price for cards. Here's a possible workaround, though.
NEW You can now price cards that you have created (either from our card creator, or by hand from the process on this page) and your customers can buy them in the shopping cart just likes prints and merchandise!