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CAPTCHA Has a Human Playing DOOM: How It Works and Why It Is Not Secure

DOOM Captcha replaces image puzzles with a tiny DOOM-style game. Here is how the four-kill challenge works, where its code lives and why bots can still beat it.
Length4 min Posted Quest giverVGSources Team
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Yes. DOOM Captcha is a real browser-based novelty CAPTCHA by Miquel Camps Orteza. Instead of identifying traffic lights or typing distorted text, you aim at enemies in a DOOM-themed scene and kill the required number before submitting a form. The documented default is four kills.

What is DOOM Captcha?

DOOM Captcha turns a CAPTCHA challenge into a tiny first-person game. A visitor starts the JavaScript challenge, shoots enemies, reaches the configured kill count and then submits the form. The project is designed as entertainment and nostalgia rather than as a serious replacement for established anti-abuse systems.

The creator’s own warning is unusually clear: the project is “a little project for fun” and, if you know how to code, “pretty easy to break the security of this.” That disclaimer should shape how anyone evaluates it.

How the challenge works

The default objective

In the documented default configuration, the player must kill four enemies. The challenge can be configured with an enemies value to change that requirement.

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#1 Best Overall
DOOM Eternal: Standard Edition - PlayStation 4
  • Gain access to the latest demon-killing Tech with the DOOM Slayer's advanced praetor suit, including a shoulder-mounted flamethrower and the retractable wrist-mounted DOOM Blade
  • Upgraded guns and mods, such as the Super shotgun's new distance-closing meat hook attachment, and abilities like the double Dash make you faster, stronger, and more versatile than ever
  • You can't Kill demons when you're Dead, and you can't stay alive without resources. These tools are the key to your survival and becoming the ultimate demon-slayer
  • A new class of (destructible) demon
  • Battle mode is the new 2 versus 1 multiplayer experience built from the ground up at id software

Available settings

  • enemies: the number of enemies that must be killed.
  • countdown: turns the countdown behavior on or off.
  • label: changes the text displayed before the CAPTCHA.

Controls and documented cheat codes

The interaction is intended for desktop browsers. The source page documents two keyboard codes: iddqd completes the CAPTCHA, while idkfa unlocks the super shotgun. These are Easter eggs, not security controls; leaving them available reinforces that the project is a playful demonstration.

Where did it come from?

Camps Orteza says he had the idea on a Friday, built the first version on Saturday morning, published it that night and went live on Sunday. He reports that it reached Product Hunt’s “TOP 1 Product of the Day.” A project update dated 26 May 2021 says John Carmack, identified on the page as a DOOM creator, liked it. The project page lists 30 May 2021 as its last update.

Rank #2
Sale
DOOM: The Dark Ages – Xbox Series X
  • Developed by id Software, DOOM: The Dark Ages is the prequel to the critically acclaimed DOOM (2016) and DOOM Eternal that tells the epic cinematic origin story of the DOOM Slayer’s rage.
  • In this third installment of the modern DOOM series, players will step into the blood-stained boots of the DOOM Slayer, in this never-before-seen dark and sinister medieval war against Hell.
  • A dark fantasy/sci-fi single-player experience that delivers the searing combat and over-the-top visuals of the incomparable DOOM franchise, powered by the latest idTech engine. With a customizable difficulty system, it’s the perfect entry point whether you’re new to the franchise or a long time fan.
  • As the super weapon of gods and kings, shred enemies with devastating favorites like the Super Shotgun while also wielding a variety of new bone-chewing weapons, including the versatile Shield Saw.
  • Experience the origin story of the DOOM Slayer’s rage in this epic, cinematic, and action-packed story.

The public repository is called DOOM Captcha and is licensed under GPL-3.0. Its README describes the demo and author and exposes the HTML, JavaScript, static assets and form pages, making the implementation available to inspect or fork. A 2025 reinterpretation is available at doom-captcha.vercel.app.

Can bots beat it?

There is no published bot-block rate, human pass rate, completion-time benchmark, accessibility study or formal security audit for DOOM Captcha. It would therefore be misleading to assign it a measured success percentage.

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Rank #3
DOOM: The Dark Ages – PlayStation 5
  • Developed by id Software, DOOM: The Dark Ages is the prequel to the critically acclaimed DOOM (2016) and DOOM Eternal that tells the epic cinematic origin story of the DOOM Slayer’s rage.
  • In this third installment of the modern DOOM series, players will step into the blood-stained boots of the DOOM Slayer, in this never-before-seen dark and sinister medieval war against Hell.
  • A dark fantasy/sci-fi single-player experience that delivers the searing combat and over-the-top visuals of the incomparable DOOM franchise, powered by the latest idTech engine. With a customizable difficulty system, it’s the perfect entry point whether you’re new to the franchise or a long time fan.
  • As the super weapon of gods and kings, shred enemies with devastating favorites like the Super Shotgun while also wielding a variety of new bone-chewing weapons, including the versatile Shield Saw.
  • Experience the origin story of the DOOM Slayer’s rage in this epic, cinematic, and action-packed story.

Its architecture nevertheless makes the limitation straightforward. The challenge runs in client-side HTML, CSS and JavaScript. In a discussion on Hacker News, commenters noted that an automated client could inspect the DOM or target pixels rather than play as a human would. Moving the game into a more difficult canvas would not, by itself, fix the problem: if the server accepts a client-controlled success callback or result without independently checking it, automation can still target that interface.

The creator’s admission that the security is easy to break is the strongest available assessment. The project is best understood as a game-shaped obstacle for casual abuse, not as a hardened proof of personhood.

Rank #4
Doom - Xbox One
  • A Relentless Campaign: There is no taking cover or stopping to regenerate health as you beat back Hell's raging demon hordes
  • Return of id Multiplayer: Dominate your opponents in DOOM's signature, fast-paced arena-style combat
  • Near-Limitless Gameplay: Doom SnapMap – A Powerful, but Easy-to-Use Game and Level Editor That Allows for Limitless Gameplay Experiences on Every Platform
  • Entertainment Software Rating Board (ESRB) Content Description: Blood and gore, intense violence, strong language

Is it suitable for a real website?

For a production signup, login, comment or checkout flow, DOOM Captcha should not be the sole anti-bot control. A responsible deployment would need all of the following:

  • Server-side verification: the server must validate challenge state and completion instead of trusting a browser callback.
  • A defined threat model: decide whether you are deterring casual scripts, coordinated automation, credential stuffing or another specific abuse pattern.
  • Abuse controls beyond the CAPTCHA: rate limits, monitoring, account and IP reputation, and appropriate session or transaction checks.
  • An accessible alternative: a reflex-based first-person game excludes or disadvantages people who cannot use a mouse, keyboard, desktop browser or fast visual interaction.
  • Device and browser testing: the documented interaction is desktop-oriented, so mobile and assistive-technology users need another path.

Without those safeguards, the novelty can add friction for legitimate visitors while offering limited resistance to a determined bot operator.

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Best Value
DOOM + DOOM II (Limited Run Games #144) - for Playstation 5
  • DOOM + DOOM II on a region-free physical disc.
  • Includes: DOOM, DOOM II, TNT: Evilution, The Plutonia Experiment, Master Levels for DOOM II, No Rest for the Living, Sigil & Sigil II, Legacy of Rust (a new episode created in collaboration by id Software, Nightdive Studios and MachineGames).
  • A new Deathmatch map pack featuring 25 maps
  • Total of 187 mission maps and 43 deathmatch maps in DOOM + DOOM II
  • # of Players: Single System 1-4, Local wireless 1-8, Online 1-16
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Support on Ko-Fi

DOOM Captcha compared with conventional CAPTCHA systems

Evaluation area DOOM Captcha What a production system must establish
Entertainment and novelty High: the visitor plays a recognizable DOOM-style challenge. Novelty is optional; effectiveness and completion rates must be demonstrated.
Transparency and forking Public GPL-3.0 source with inspectable HTML, JavaScript and assets. Open code can aid review, but does not prove resistance to automation.
Resistance to DOM, pixel and callback automation Not established; technical discussion identifies plausible automation paths. Independent testing and server-side validation are required.
Accessibility and device support Desktop game interaction; no published accessibility study. Provide an accessible, usable alternative and test supported devices.
Independent server verification No evidence in the available material of a production-grade verification design. The server must verify the result and enforce the surrounding abuse controls.

The comparison is qualitative. No controlled benchmark supports a numerical ranking against conventional CAPTCHA products.

Where can developers inspect the code?

The DOOM Captcha repository is public under GPL-3.0 and includes the client pages, JavaScript and static assets needed to understand or fork the demo. The README also points to the live demo and author. The separately hosted 2025 reinterpretation is at doom-captcha.vercel.app. Check the repository’s current README and license before redistributing a modified version.

Why the project still matters

DOOM Captcha succeeds on its actual goal: it makes a routine web gate memorable. It demonstrates how a familiar game mechanic can turn a CAPTCHA into a shareable joke, and its open implementation gives developers a compact example to study. Its value is creative and nostalgic, not evidence that playing a game is a secure substitute for server-validated anti-abuse design.

The Bottom Line

Bottom line: DOOM Captcha is a genuine, public and configurable browser game CAPTCHA—normally four enemy kills—but its creator says it is easy to break, and no independent benchmark or audit establishes production security. Use it as a novelty demo, not as the only defense on a real website.

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Quick Recap

Bestseller No. 1
DOOM Eternal: Standard Edition - PlayStation 4
DOOM Eternal: Standard Edition - PlayStation 4
A new class of (destructible) demon
$27.49
SaleBestseller No. 2
Bestseller No. 4
Bestseller No. 5
DOOM + DOOM II (Limited Run Games #144) - for Playstation 5
DOOM + DOOM II (Limited Run Games #144) - for Playstation 5
DOOM + DOOM II on a region-free physical disc.; A new Deathmatch map pack featuring 25 maps
$44.62

Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.

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