Place the photo
Now it's time to position the picture in the card's "canvas." We'll do that by setting the background of the photo to the correct size. First, choose Image, Resize, Canvas Size. Enter the width and height of the closed greeting card, which in our case has a width of 3 inches and a height of 4 inches. Click OK. You should see the photo centered in a rectangular canvas--like the front of the greeting card.
Next, you need to rxtend the canvas horizontally to the full width of an open greeting card. Again choose Image, Resize, Canvas Size; but this time change the width to 6 inches. Click the right-middle anchor tile to instruct Photoshop to expand the canvas to the left. Then click OK.