I had my visa appointment last Thursday and then had a bit of a panic this morning when I was sorting through the folder that I took with me. I realized that at no point during the process was I asked for a hard copy of my passport photo. The two that I had taken with me were still in their little pouch at the back of my folder.
I immediately called the embassy, but all morning I kept getting the automated message that said "we are currently experiencing high call volumes and are unable to answer your call at this time." I finally got through a minute ago and spoke to someone.
Apparently nowadays they only ask you to take printed passport photos in case the digital photo you upload while filling out the DS-160 isn't right for some reason. I had figured that this would be the case but with US government processes you can never tell if they'll follow the logical path or not. Anyway, panic over.
Advice - If you get home after your appointment and find that you still have your passport photo's then don't worry, as long as you uploaded a good digital photo to the DS-160 then you're fine.