In various versions of the meme, people were instructed to post their first profile picture alongside their current profile picture, or a picture from 10 years ago alongside their current profile picture.
So, yes: These profile pictures exist, they’ve got upload time stamps, many people have a lot of them, and for the most part they’re publicly accessible. Imagine that you wanted to train a facial recognition algorithm on age-related characteristics and, more specifically, on age progression (e.g., how people are likely to look as they get older).
That application isn’t very exciting, but stands to make advertising more relevant.
But as that data flows downstream and becomes enmeshed with our location tracking, response and purchase behavior, and other signals, it could bring about some genuinely creepy interactions.
Even the EXIF metadata on the photo wouldn't always be reliable for assessing that date. Some people resort to uploading screenshots of pictures found elsewhere online. Through the Facebook meme, most people have been helpfully adding that context back in (“me in 2008 and me in 2018”) as well as further info, in many cases, about where and how the pic was taken (“2008 at University of Whatever, taken by Joe; 2018 visiting New City for this year’s such-and-such event”).
In other words, thanks to this meme, there’s now a very large dataset of carefully curated photos of people from roughly 10 years ago and now.
Facial recognition's potential is mostly mundane: Age recognition is probably most useful for targeted advertising.
Ad displays that incorporate cameras or sensors and can adapt their messaging for age-group demographics (as well as other visually recognizable characteristics and discernible contexts) will likely be commonplace before very long.
Ideally, you'd want a broad and rigorous dataset with lots of people's pictures.
It would help if you knew they were taken a fixed number of years apart—say, 10 years.