On my doll & sewing groups the most requested change from members during the past few year is being able to add Comments to other members' posted photos.
When introduced by y***o, how quickly became a boon to those groups. It was easier for busier members to keep up with the number of emails. It concentrated the message posts down to the most important ones by nearly eliminating those that said 'your photo is nice' & the obligatory 'thanks' replies.
Also turned out to be good for future research projects by keeping others' notes available with the picture long after the posting date. No need to hunt for message posts.
I respectfully thank you for the ability to make the suggestion & your consideration.