You’ll see it is super easy to create U.S. passport size (2″x2″) photos, which is what you need for green card purpose as well. There are a few different print options but you can choose the “do it yourself” option which is by far the cheapest. Save a local copy to your computer, and you can then bring it to a Walgreens, CVS, Target etc. on a USB stick to be printed out for a few cents. Some stores even allow you to upload them via their website and pick them up for no extra charge.