A lightweight, anti-OCR dot-matrix CAPTCHA system designed to prevent automated bot recognition through distorted text rendering. Developed by the system_mini member of EndlessPixel Studio.

This project implements a server-side CAPTCHA system that generates dot-matrix style verification codes with random distortions to resist OCR-based attacks. It provides both the image generation frontend and verification backend.

• Dot Matrix Characters: Uses a custom 5x3 dot matrix pattern for alphanumeric characters
• Anti-OCR Protection: Random rotation, noise dots, and positional jitter
• Server-Side Validation: Secure token-based verification system
• Simple API: RESTful endpoints for verification and status checks
• Lightweight: Minimal dependencies, easy to deploy

1. Clone the repository:

# use Git to clone the repository git clone https://github.com/EndlessPixel/captcha.git # or use GitHub CLI gh repo clone EndlessPixel/captcha # change directory to the project folder cd captcha

2. Start the server:

# start the server node server.js

The server will run on port 3000 by default.

1. Get CAPTCHA

• Endpoint: GET /get-captcha
• Response: SVG format CAPTCHA image

2. CAPTCHA Verification

• Endpoint: POST /verify
• Content-Type: application/x-www-form-urlencoded
• Parameters:
  • userCode: User-input CAPTCHA code
• Success Response:

{ "success": true, "message": "Verification successful", "uid": "xxxx-xxxx-xxxx-xxxx-xxxx" }

• Error Response:

{ "success": false, "message": "Verification code error" }

3. Verification Status Check

• Endpoint: GET /inquire?uid={verification_uid}
• Parameters:
  • uid: Verification UID received from /verify endpoint
• Response: Returns true if verified, false if not

1. Get CAPTCHA (API)

• Endpoint: GET /api/captcha
• Response: JSON format with token and base64-encoded CAPTCHA image

{ "success": true, "token": "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx", "captcha": "data:image/svg+xml;base64,..." }

2. CAPTCHA Verification (API)

• Endpoint: POST /api/verify
• Content-Type: application/x-www-form-urlencoded
• Parameters:
  • userCode: User-input CAPTCHA code
  • token: Token received from /api/captcha endpoint
• Success Response:

{ "success": true, "message": "Verification successful", "uid": "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx" }

3. Verification Status Check (API)

• Endpoint: GET /api/inquire?uid={verification_uid}
• Parameters:
  • uid: Verification UID received from /api/verify endpoint
• Response:

{ "success": true, "verified": true }

Visit http://localhost:3000 to use the web-based CAPTCHA system.

<!-- Add a div container in your page --> <div id="captcha-container"></div> <!-- Include the CAPTCHA SDK --> <script src="/captcha-sdk.js"></script>

// Custom configuration window.initCaptcha({ containerId: 'custom-captcha', // Custom container ID onSuccess: function(uid) { console.log('Verification successful, UID:', uid); // Handle successful verification }, onError: function(message) { console.log('Verification failed:', message); // Handle verification failure }, onExpire: function() { console.log('CAPTCHA expired'); // Handle expired CAPTCHA } });

const response = await fetch('/api/captcha', { method: 'GET' }); const result = await response.json(); // Use result.token and result.captcha

const response = await fetch('/api/verify', { method: 'POST', headers: { 'Content-Type': 'application/x-www-form-urlencoded' }, body: new URLSearchParams({ userCode: 'ABCD', token: 'xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx' }) }); const result = await response.json(); // Use result.uid for status checks

const response = await fetch('/api/inquire?uid=xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx', { method: 'GET' }); const result = await response.json(); // Check result.verified

• Server port (default: 3000)
• Verification token storage and expiration
• CAPTCHA character set

• Server-side validation prevents client-side tampering
• Verification tokens are randomly generated and stored
• Implement rate limiting in production environments

• Chrome: 60+
• Firefox: 55+
• Safari: 11+
• Edge: 79+

captcha/ # Dot Matrix CAPTCHA project folder ├─┬── docs/ # Documentation and examples │ ├── api.html # API usage example │ └── sdk-demo.html # SDK usage example ├──── index.html # Main HTML file ├──── server.js # Node.js server ├─┬── public/ # Public assets │ ├── style.css # Stylesheet │ ├── script.js # Frontend logic │ └── captcha-sdk.js # CAPTCHA SDK ├──── LICENSE # MIT License └──── README.md # This file 

MIT License © 2024-2026 EndlessPixel Studio

• Project URL: https://github.com/EndlessPixel/captcha
• Developer: system_mini (EndlessPixel Studio)