Once you've chosen the design, first click on the center of the card. Next, click the blue "Add Photo" button at the top of the page to upload an image from your computer or device.
Then, just drag your image to the card and use the +/- buttons to zoom in or out.
Click the green Done button, edit the text if you like and you'll be all set with your personalized, custom digital card!
Using a Photo Design requires an Extra level membership. Uploading a logo would require a Business level membership. See here for more info. Logos are placed on the digital card envelope.