All of your photos should be in a JPEG format. You can tell by their file extension ".jpg". If you can help it, they should also have a resolution of 300dpi. I don't want to bog you down with this so just feel safe that if you took the picture with a digital camera, you shouldn't experience problems. You can upload photos from any page where a photo can be placed. This includes the front and back cover. To upload a photo, click the "edit" button and head to the "Picture" tab.
You'll see an "Upload" Button. Click on it and a file explorer window comes up so you can locate your files on your computer. Once you’ve selected the photos you wish to upload, click on the “Open” button and you should then see status bars appear for your selected photos. Once the uploading has finished, you should see your picture(s) appear in your photo gallery. Click on it, and an orange border will appear indicating it is selected. You also have access to millions of stock photos that can be added to your cookbook.