1. Remove the photographs they've commented on (or just the comments if you can do that) so that they don't have any "bait."
2. Remember that you're a lot more <insert suitable adjective here, examples may include pretty, clever, mature...> than them.
3. If you really want to say something to them, please don't be bitchy or lower yourself to their level. Something like you don't appreciate the comments and you'd like it if they kept their opinions to themselves.
4. Try to ignore it. If you respond, they'll keep on going as they're getting what they want; a reaction.