Tip #1: Select background images that are 1024 x 768 minimum recommended resolution for 4x6 (if it's less, you may find your images pixilated.
Tip # 2: You can add more than one layer to a photo. If you want to add accessories, make sure you find an image that has a transparent background (PNG).
Tip #3: I have the best luck by opening the background first and then adding Layers (Import From File).
Here are some examples that I created as an example: