Creating a Captcha Form

This PHP program demonstrates how to create a captcha form with the Graphics Draw, GD, library.
Captcha.php

<!DOCTYPE html>
<html>
  <head>
    <title>XoaX.net PHP</title>
  </head>
  <body style="background-color:#F0F0E0;">
<?php
  session_start();
  $_SESSION['Time']=time();
  // Check that the form text was submitted
  if (isset($_POST["qInput"])) {
    $sInput = $_POST["qInput"];
    // Check that the correct text was entered
    if (isset($_SESSION['CaptchaCode']) && $sInput == $_SESSION['CaptchaCode']) {
      DisplayCorrect();
      return;
    } else {
      DisplayIncorrect();
    }
  }
  // Display the initial page
  CreateCaptchaImageAndDisplayForm();
?>
  </body>
</html>


<?php
  function DisplayCorrect() {
?>
    <div style="text-align:center;">
      <h1>Your answer is correct!</h1>
      <form action=" <?php echo $_SERVER['PHP_SELF']; ?>" method="POST">
        <input type="submit" value="Refresh the Page">
      </form>
    </div>
<?php
  }
?>

<?php
  function DisplayIncorrect() {
?>
    <div style="text-align:center;">
      <h1>Your answer is incorrect!<br>please try again </h1>
    </div>
<?php
  }
?>

<?php
  function CreateCaptchaImageAndDisplayForm() {
    $iImageWidth = 200;
    $iImageHeight = 50;
    $qCaptchaImage = ImageCreateTrueColor($iImageWidth, $iImageHeight);
    $qBkgdColor = ImageColorAllocate($qCaptchaImage, 255, 255, 255);
    // Draw the background color
    ImageFilledRectangle($qCaptchaImage, 0, 0, $iImageWidth, $iImageHeight, $qBkgdColor);
    // Draw lines to obscure the text
    $qLineColor = ImageColorAllocate($qCaptchaImage, 64, 64, 64);
    for ($i = 0; $i < 10; ++$i) {
      ImageLine($qCaptchaImage, 0, rand()%50, 200, rand()%50, $qLineColor);
    }
    // Draw some random pixels to obscure the text
    $qPixelColor = ImageColorAllocate($qCaptchaImage, 0, 0, 255);
    for ($i = 0; $i < 1000; ++$i) {
      ImageSetPixel($qCaptchaImage, rand()%200, rand()%50, $qPixelColor);
    }

    // Generate the code
    $sChars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz';
    $iCount = strlen($sChars);
    $qCharColor = ImageColorAllocate($qCaptchaImage, 0, 0, 0);
    $sCode = '';
    for ($i = 0; $i < 6; ++$i) {
      $sChar = $sChars[rand(0, $iCount - 1)];
      ImageString($qCaptchaImage, 5, 25 + ($i * 30), 15 + (rand()%5), $sChar, $qCharColor);
      $sCode .= $sChar;
    }
    $_SESSION['CaptchaCode'] = $sCode;

    // Remove the old saved files.
    $qaImageFiles = glob("*.png");
    foreach($qaImageFiles as $qOldFile) {
      unlink($qOldFile);
    }
    // Save the png image file
    ImagePNG($qCaptchaImage, "captcha".$_SESSION['Time'].".png");
?>
    <div style="text-align:center;border:1px black solid;padding:5px;background-color:#FFFFEE;">
      <h3>Enter the text in this image to verify that you are human.</h3>
      <b>Refresh the page if you can not read the letters.</b>
      <div style="display:block;margin-bottom:20px;margin-top:20px;">
        <img src="captcha<?php echo $_SESSION['Time']?>.png">
      </div>
      <form action=" <?php echo $_SERVER['PHP_SELF']; ?>" method="POST">
        <input type="text" name="qInput"/>
        <input type="submit" value="Submit" name="qSubmit"/>
      </form><br />
      <form action=" <?php echo $_SERVER['PHP_SELF']; ?>" method="POST">
        <input type="submit" value="Refresh the Page">
      </form>
    </div>
<?php
  }
?>
GD PHP

Creating a Captcha Form

Captcha.php

Output
