Facebook already has access to a larger repository of photos going back over a decade and all the years inbetween along with decent face recognition to create a much bigger dataset than resorting to a hashtag challenge. But I guess that wouldn't be newsworthy.
This was addressed in the article:
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.
But let's play out this idea.
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). 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.
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In other words, it would help if you had a clean, simple, helpfully labeled set of then-and-now photos.