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Captcha with arithmetic's questions

/ Published in: PHP
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Save this snippet as .php file and use it as image source.
This captcha code shows random arithmetic's questions.
You can download needed font from http://www.1001fonts.com/font_details.html?font_id=2939

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Copy this code and paste it in your HTML 
  1. session_start();
  2. header("Content-type: image/png");
  3. $width = 120;
  4. $height = 30;
  5. $im = @imagecreate($width, $height)
  6.     or die("Cannot Initialize new GD image stream");
  7. imagecolorallocate($im, 247, 250, 233);
  8. $noise_color = imagecolorallocate($im, 253, 175, 90);
  9. 	for( $i=0; $i<($width*$height)/3; $i++ ) {
  10.          imagefilledellipse($im, mt_rand(0,$width), mt_rand(0,$height), 1, 1, $noise_color);
  11.       }
  12.       /* generate random lines in background */
  13.       for( $i=0; $i<($width*$height)/120; $i++ ) {
  14.          imageline($im, mt_rand(0,$width), mt_rand(0,$height), mt_rand(0,$width), mt_rand(0,$height), $noise_color);
  15.       }
  16. $text_color = imagecolorallocate($im, 175, 102, 43);
  17.  
  18.  
  19. $action = array('+', '*', '-');
  20. shuffle($action);
  21. if($action[0] == '+') {
  22. 	$a = rand(1, 9);
  23. 	$b = rand(1, 9);
  24. 	$_SESSION['code'] = $a + $b;
  25. }
  26. elseif($action[0] == '*') {
  27. 	$a = rand(1, 9);
  28. 	$b = rand(1, 9);
  29. 	$_SESSION['code'] = $a * $b;
  30. }
  31. elseif($action[0] == '-') {
  32. 	$b = rand(1, 9);
  33. 	$c = $b+1;
  34. 	$a = rand($c, 9);
  35.  
  36. 	$_SESSION['code'] = $a - $b;
  37. }
  38.  
  39. $text = $a.$action[0].$b;
  40.  
  41. for($j = 0; $j < strlen($text); $j++) {
  42. 	$angle = rand(-20, 20);
  43. 	imagettftext($im, 18, $angle, 29+($j*23), (18+(($height-18)/2)), $text_color, './WC_Wunderbach_Rough.ttf', $text[$j] );
  44. }
  45. imagepng($im);
  46. imagedestroy($im);
  47.  
  48. //usage : save this snippet as captcha.php file and use it that
  49. //point it as image source 
  50. //<img src="captcha.php" />
  51. //to check is it passed correctly, do following
  52. //if(isset($_SESSION['code']) && ($_POST['captcha'] == $_SESSION['code'])) 
  53. //its needed to check is $_SESSION['code'] is set, because if somebody block
  54. //the image loading, the check ($_POST['captcha'] == $_SESSION['code']) will 
  55. //return false positive if the form is sent with empty captcha field

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