For each photo, I put the Sponsor's full name and date of birth as well as the Applicant's full name and date of birth. Other people depicted in any of the pictures were also listed (just name, and whether family member, friend, acquaintance, etc)
We also inserted each photo (or sometimes 2 smaller photos) in MS Word on a regular sized page and were able to have enough room to type the necessary information and a small explanation of what the photo was about.