7DBW - Seven days of black and white photos Photography
At the risk of joining the ranks of food and latte photographers, I chipped in.
Not too much of a challenge, of course, but a bit of fun, even though the likes of Slate, as well as a few bloggers here and there, can't appreciate it too much.
This chained photo exercise gained steam only just now, in October 2017, though I couldn't find a source. I went back up my chain, but after only a few steps got to a person without a Facebook account, or so it seemed.
A much more cringeworthy, but somewhat similar, 'challenge' was popular about a year ago, where participants were posting black and white selfies, with the text "challenge accepted".
Further back, quite a similar photo exercise did the round of posting five black and white photos on five consecutive days, though, here, no additional 'rules' seemed to have been attached, resulting in participants 'just' including their best work in black and white.