How old are they, how many people are in the photos, are they recognizable, and where will you post them? There is a "rule of three or more" that tends to come into play, when you have a group, if you're not naming them, that you can run it without permission. But this is a pretty squishy "rule."
If you know you have someone who hates to have their photo taken, then I'd say play it safe and avoid posting any photos where they are recognizable.