Slay imps, monitor stocks, to prove you are human

The game Doom has, over time, turned up everywhere.

- K Narayanan

It's been retrofitted, by fans, for iPods and digital cameras, ATM machines and calculators; within Excel spreadsheets and even in the display screen of a pregnancy test.So it isn't surprising that there's a kind of CAPTCHA in which the user plays Doom to prove they are human. The premise is simple: kill three enemies.

But it isn't as easy as it looks. Move forward, and you may be destroyed by fireball-throwing imps. Far better to camp at starting position and wait for the enemies to approach. I did this, and it took me two tries to clear the test. The game, devised in 2021 by programmer Miquel Camps Orteza as a way to showcase his skill, is the simplest in a small but intriguing sub-genre.

CAPTCHA, that annoying genre of online tests that screens for bots by demanding that all users type out letters, or click on ail the images of bicycle wheels, has spawned a host of online games, some of which play out over hours.