While you can magically find photos with any given number of people on Facebook, clicking on them (in Google’s image search) lands on the page, not the photo itself. You have to scroll down to find it. As I have found out, to find “just” photos (or rather, pages with one photo only), you need to X-Ray in a more specific manner, namely,
site:facebook.com/*/photos/a (add your keywords).
Here is an example of precise people counting by Facebook. Another example (suppose I am sourcing in Healthcare):
site:facebook.com chicago hospital “from left to right” “image may contain * people”. You can see a screenshot of the results above.
Once you land on a page with the photo in question, you will often see who who has posted it and often, who is on the photo, who liked it, and who commented.
You can find pages like these:
You can then collect the data and engage with selected “likers”.
(To narrow to profile photos, if you were wondering, try this: site:facebook.com/*/photos/a “updated their profile photo”.)
My example strings find images but you can, of course, run them in “all” searches.