How do I upload photos from Google Photos?
In addition to using photos from your computer or mobile devices, Collage.com has made it easy to add images from Google Photos
All of Collage.com's upload options can be found by clicking to the left of an open project or below the project for mobile users. (You'd click on book or calendar projects).
You'd then click "Google Photos" from the list of options to be prompted to login to your Google Photos account.
Login with your Google Photos credentials, and then click "Allow" when prompted to allow Collage access.
Then, you're Google Photos uploads will appear in folders for you to add to your project.