Building a CAPTCHA Generator with JavaScript, HTML, and CSS
December 16, 2024 • 4 min read

Building a CAPTCHA Generator with JavaScript, HTML, and CSS

Web developmentJavaScriptCSS3Programming
share this article on
In this tutorial, we'll create a CAPTCHA generator tool using JavaScript, HTML, and CSS. The tool will feature a user-friendly UI and provide functionality to generate and verify CAPTCHAs. This can be a fun project for beginners and a useful addition to secure web forms.

Features of the CAPTCHA Tool:

  1. User Interface: A modern card with a title, CAPTCHA display, input field, and buttons styled with CSS.
  2. Captcha Features:
  1. Verification System: Validate user input and display success or error messages.

Step 1: Setting Up the HTML Structure

The HTML structure contains a container for the CAPTCHA, an input field, and buttons for user interaction.

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Captcha Generator</title>
  <link rel="stylesheet" href="styles.css">
</head>
<body>
  <div class="captcha-container">
    <h1>Captcha Generator</h1>
    <div class="captcha-display">
      <canvas id="captchaCanvas" width="200" height="50"></canvas>
      <div class="captcha-actions">
        <button id="refreshCaptcha" aria-label="Generate New Captcha">🔄</button>
        <button id="readCaptcha" aria-label="Read Captcha">🔊</button>
      </div>
    </div>
    <input type="text" id="captchaInput" placeholder="Enter captcha here">
    <button id="verifyCaptcha">Verify Captcha</button>
    <p id="captchaMessage"></p>
  </div>
  <script src="script.js"></script>
</body>
</html>

Explanation:

Step 2: Styling with CSS

The CSS ensures a responsive, modern UI with clear visual feedback.

body {
    margin: 0;
    font-family: Arial, sans-serif;
    background-color: #333;
    color: #fff;
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
}

h1 {
    margin-bottom: 2.5rem;
}

.captcha-container {
    text-align: center;
    background-color: #444;
    padding: 20px;
    border-radius: 8px;
    box-shadow: 0 0 10px rgba(0, 0, 0, 0.5);
    width: 300px;
}

.captcha-display {
    display: flex;
    align-items: center;
    justify-content: center;
    margin-bottom: 20px;
    border-radius: 15px;
}

canvas {
    background-color: #fff;
    text-decoration: line-through;
    font-size: 20px;
    letter-spacing: 2px;
}


input[type="text"] {
    width: calc(100% - 20px);
    padding: 10px;
    margin-bottom: 10px;
    border: none;
    border-radius: 5px;
}

button {
    padding: 10px 15px;
    background-color: #555;
    color: #fff;
    border: none;
    border-radius: 5px;
    cursor: pointer;
}

button:hover {
    background-color: #666;
}

#captchaMessage {
    margin-top: 10px;
}

.captcha-actions {
    display: inline-flex;
    align-items: center;
    gap: 10px;
}

.captcha-actions button {
    display: flex;
    align-items: center;
    justify-content: center;
    margin-left: 10px;
    width: 30px;
    height: 30px;
    background-color: #555;
    border-radius: 50%;
    border: none;
    cursor: pointer;
    color: #fff;
    font-size: 18px;
}

.captcha-actions button:hover {
    background-color: #666;
}

#captchaCanvas {
    border-radius: 5px;
}

#captchaInput {
    height: 30px;
}

#verifyCaptcha {
    width: 100%;
    padding: 15px;
    margin: 15px 0;
    background-color: #2fa3e9;
    color: #fff;
    font-size: 15px;
    font-weight: bold;
    border: none;
    border-radius: 5px;
    cursor: pointer;
}

#verifyCaptcha:hover {
    background-color: #2491d4;
}

Key Features:

Step 3: Adding Functionality with JavaScript

The JavaScript handles CAPTCHA generation, rendering, validation, and reading aloud.

const canvas = document.getElementById("captchaCanvas");
const ctx = canvas.getContext("2d");
const refreshCaptcha = document.getElementById("refreshCaptcha");
const readCaptcha = document.getElementById("readCaptcha")
const captchaInput = document.getElementById("captchaInput")
const verifyCaptcha = document.getElementById("verifyCaptcha");
const capthcaMessage = document.getElementById("captchaMessage");

let generatedCaptcha = "";

function generateCaptcha() {
  generatedCaptcha = Math.random().toString(36).substring(2, 8);
  renderCaptcha();
}

function renderCaptcha() {
  ctx.clearRect(0, 0, canvas.width, canvas.height);
  ctx.font = "30px Arial";
  ctx.fillStyle = "#000";
  ctx.fillText(generatedCaptcha, 20, 35);

  const textWidth = ctx.measureText(generatedCaptcha).width;
  ctx.strokeStyle = "#f00";
  ctx.lineWidth = 2;
  ctx.beginPath();
  ctx.moveTo(20, 25);
  ctx.lineTo(20 + textWidth, 25);
  ctx.stroke();
}

verifyCaptcha.addEventListener("click", () => {
  const userInput = captchaInput.value.trim();
  if (userInput === generatedCaptcha) {
    captchaMessage.textContent = "You have entered the correct captcha!";
    captchaMessage.style.color = "#00ff00";
  } else {
    captchaMessage.textContent = "Incorrect captcha. Try again.";
    captchaMessage.style.color = "#ff0000";
  }
});

refreshCaptcha.addEventListener("click", generateCaptcha);

readCaptcha.addEventListener("click", () => {
  const utterance = new SpeechSynthesisUtterance(generatedCaptcha);
  speechSynthesis.speak(utterance);
});

generateCaptcha();

Key Functionalities:

  1. Generate CAPTCHA:
  1. Refresh and Read CAPTCHA:
  1. Verification:

Conclusion

This CAPTCHA generator is a great addition to your web projects and a fun way to learn HTML, CSS, and JavaScript. Try customizing it further for advanced use cases like integrating it into a form submission process.

Back to Articles