On the Photos page click Edit Photo 1 or Edit Photo 2.
You will be prompted to select a photo on your device. NOTE: if you are using Poply on a phone or tablet, you will also have the option to take a picture.
Once you have selected a photo, you will be taken to an editing screen where you can rotate your photo if you need to and select the portion of the photo that will display on your invitation. When you are finished editing your photo, click Save.