How do you tag someone in a picture on Facebook?

[J.R.]

How do you tag someone into a picture like this? I try to tag myself into it but it said "Can't find any faces to tag" what does that even mean? how do you tag someone into this picture?
Also, when i try to use the Tag my pals app or to to the actual website of Tag My Pals, it doesn't work

[John Smith]

Just click on the photo and click "Tag Photo". Type out the names of people who want to see your photo or be associated with it. You can tag yourself too. Facebook often hints on tagging faces if they appear in your pic. If you are a business page, you have to use the profile page to tag your pals. If you still can't, refresh the Facebook page