My working theory: The photos that received the most likes and comments had three things in common 1) featured an old friend or a well-known person 2) there’s a surprise factor 3) posted after at least 20 days of not posting.  The quality and color of the photo were secondary factors. The photos that had the fewest engagements were the ones with minimal context, featured unknown people, or followed a recent post. When I designed my three new photos, I made sure to post unexpected photos that included an old friend or family member.