There are all kinds of CAPTCHAs out there: unscramble the characters, identify the object, count the cats, classify items, move the slider, and so on. Many of them are rather transparently crowdsourced AI training data. That’s not the case with the latest CAPTCHA, though, which challenges users to kill three enemies in a game of classic DOOM.
Sounds easy, right? Well, it is, if you’re a DOOM veteran. The challenge is this: pistol start Episode 1’s secret level, Military Base, and get three kills. The ‘catch’ is that it’s on Nightmare difficulty. For those who know their DOOM lore, one of the changes in Nightmare difficulty removes the delay before and between enemy attacks, allowing (indeed, forcing) ranged attackers to continue unloading their weapons or flinging fireballs at a blistering pace. Oh, and projectiles also move three times as fast. Have fun!
There is a trick to the challenge, if you know the level; simply fire your gun once to wake up the enemies in the surrounding hallways, and then use the relative accuracy of your pistol to wear down a few of them from a safe distance. With some care, it’s even possible to do this without taking damage. However, if you run out into the center area in full view of the caged imps (who might as well be caged machinegunners, on Nightmare mode), you will be incinerated extremely quickly.
The CAPTCHA implements the free-to-distribute shareware episode of DOOM, and the implementation is complete, to the degree that the original cheat codes even work. You can type IDCLEVxy (where x and y are single numbers 1-3 and 1-9 respectively) to change levels, although only Episode 1 is available and the game ends after you kill 3 monsters regardless. You can also use IDDQD for God mode if you’re struggling.
The developers of the DOOM CAPTCHA did make some changes to the game; the game is using a non-default sound pack of some sort, and they implemented some new command-line switches that automatically revive the dead player after two seconds and prevent the player from opening the main menu. Otherwise, though, it’s just DOOM, albeit with only keyboard controls. There’s even mobile support of some sort, although we didn’t test it.
As to the efficacy of DOOM as a CAPTCHA, well, we can’t say. Many CAPTCHAs that are difficult for humans are actually very easy for bots, and there have been bots that can play FPS games quite skillfully nearly as long as there have been FPS games. It’s difficult to imagine that this method of proving one’s humanity is particularly effective. Still, it’s quite entertaining; kudos to the developers for a solid laugh.
By the way, if you haven’t played DOOM recently, grab the excellent DOOM + DOOM II re-release from last year on Steam, which uses a custom-rewritten multi-core software renderer that supports high frame rates and resolutions. It also comes with a killer new episode that has some gameplay changes. The new release includes all official classic DOOM content as well as many user mods, and it’s only ten bucks.