PHP | Noureddine's El-Zaatari Blog

PHP Contact form with image verification

July 22nd, 2007 Noor

In this tutorial im going to show to add an image verification code Captcha to your contact form to avoid Spam in easy steps.

In the php file where you are verifying the captcha image and processing other information place the following code preferably at the top of the page since that we are going to use sessions.

Verrifying th image can be done this way:

The following code should be save as imagebuilder.php where here we create the image, the code is commented as you have notices with lots of tweaks to customize it the way you need but i have just kept it as simple as possible.

include "settings.php";
// Keep #'s reasonable.
$min_thickness = max(1,$min_thickness);
$max_thickness = min(20,$max_thickness);
// Make radii into height/width
$min_radius *= 2;
$max_radius *= 2;
// Renormalize contrast
$contrast = 255 * ($contrast / 100.0);
$o_contrast = 1.3 * $contrast;

$width = 15 * imagefontwidth (5);
$height = 2.5 * imagefontheight (5);
$image = imagecreatetruecolor ($width, $height);
imagealphablending($image, true);
$black = imagecolorallocatealpha($image,3,2,44,5);

// Build the  validation string
$max = strlen($acceptedChars)-1;
$password = NULL;
for($i=0; $i < $stringlength; $i++) {
$cnum[$i] = $acceptedChars{mt_rand(0, $max)};
// the following generates the characters to be displayed on the image
$password .= $cnum[$i];
}

// Add string to image
$rotated = imagecreatetruecolor (70, 70);
for ($i = 0; $i < $stringlength; $i++) {
$buffer = imagecreatetruecolor (20, 20);
$buffer2 = imagecreatetruecolor (40, 40);

// Get a random color
$red = 255;
$green = 255;
$blue = 255;
$color = imagecolorallocate ($buffer, $red, $green, $blue);

// Create character
imagestring($buffer, 5, 0, 0, $cnum[$i], $color);

// Resize character
imagecopyresized ($buffer2, $buffer, 0, 0, 0, 0, 30, 30, 20, 20);

// Rotate characters a little
$rotated = imagerotate($buffer2, 0,imagecolorallocatealpha($buffer2,0,0,0,0));
imagecolortransparent ($rotated, imagecolorallocatealpha($rotated,0,0,0,0));

// Move characters around a little
$y = mt_rand(1, 3);
$x += mt_rand(2, 6);
imagecopymerge ($image, $rotated, $x, $y, 0, 0, 40, 40, 100);
$x += 22;

imagedestroy ($buffer);
imagedestroy ($buffer2);
}

// Draw polygons
if ($num_polygons > 0) for ($i = 0; $i < $num_polygons; $i++) {
$vertices = array (
mt_rand(-0.25*$width,$width*1.25),mt_rand(-0.25*$width,$width*1.25),
mt_rand(-0.25*$width,$width*1.25),mt_rand(-0.25*$width,$width*1.25),
mt_rand(-0.25*$width,$width*1.25),mt_rand(-0.25*$width,$width*1.25)
);
$color = imagecolorallocatealpha ($image, mt_rand(0,$o_contrast), mt_rand(0,$o_contrast), mt_rand(0,$o_contrast), $object_alpha);
imagefilledpolygon($image, $vertices, 3, $color);
}

// Draw random circles
if ($num_ellipses > 0) for ($i = 0; $i < $num_ellipses; $i++) {
$x1 = mt_rand(0,$width);
$y1 = mt_rand(0,$height);
$color = imagecolorallocatealpha ($image, mt_rand(0,$o_contrast), mt_rand(0,$o_contrast), mt_rand(0,$o_contrast), $object_alpha);
//	$color = imagecolorallocate($image, mt_rand(0,$o_contrast), mt_rand(0,$o_contrast), mt_rand(0,$o_contrast));
imagefilledellipse($image, $x1, $y1, mt_rand($min_radius,$max_radius), mt_rand($min_radius,$max_radius), $color);
}

// Draw random lines
if ($num_lines > 0) for ($i = 0; $i < $num_lines; $i++) {
$x1 = mt_rand(-$width*0.25,$width*1.25);
$y1 = mt_rand(-$height*0.25,$height*1.25);
$x2 = mt_rand(-$width*0.25,$width*1.25);
$y2 = mt_rand(-$height*0.25,$height*1.25);
$color = imagecolorallocatealpha ($image, mt_rand(0,$o_contrast), mt_rand(0,$o_contrast), mt_rand(0,$o_contrast), $object_alpha);
imagesetthickness ($image, mt_rand($min_thickness,$max_thickness));
imageline($image, $x1, $y1, $x2, $y2 , $color);
}

// Draw random dots
if ($num_dots > 0) for ($i = 0; $i < $num_dots; $i++) {
$x1 = mt_rand(0,$width);
$y1 = mt_rand(0,$height);
$color = imagecolorallocatealpha ($image, mt_rand(0,$o_contrast), mt_rand(0,$o_contrast), mt_rand(0,$o_contrast),$object_alpha);
imagesetpixel($image, $x1, $y1, $color);
}

session_start();
$_SESSION['string'] = $password;

header('Content-type: image/png');
imagepng($image);
imagedestroy($image);

Notice the at the end of the code

where here we are instantiating a session variable that will store the password and will use while processing the form

save the following code as settings.php where it contains variables to be used by the imagebuilder.php

// This string contains allowable characters for the image.
// To reduce confusion, zero and the letter 'o' have been removed,
// and QuickCaptcha is NOT case-sensitive.
$acceptedChars = 'ABCDEFGHIJKLMNPQRSTUVWXYZ123456789';

// Number of characters in image.
$stringlength = 5;

// A value between 0 and 100 describing how much color overlap
// there is between text and other objects.  Lower is more
// secure against bots, but also harder to read.
$contrast = 5;

// Various obfuscation techniques.
$num_polygons = 0; // Number of triangles to draw.  0 = none
$num_ellipses = 0;  // Number of ellipses to draw.  0 = none
$num_lines = 0;  // Number of lines to draw.  0 = none
$num_dots = 0;  // Number of dots to draw.  0 = none

$min_thickness = 20;  // Minimum thickness in pixels of lines
$max_thickness = 20;  // Maximum thickness in pixles of lines
$min_radius = 5;  // Minimum radius in pixels of ellipses
$max_radius = 5;  // Maximum radius in pixels of ellipses

// How opaque should the obscuring objects be. 0 is opaque, 127
// is transparent.
$object_alpha = 5;

Now finally its time to place the image and a in the main contact form with a textbox to enter the verification code of the image

place the following code where you want the image to appear

echo ‘<p><a href=”http://’.$_SERVER[’HTTP_HOST’].htmlentities($_SERVER[’PHP_SELF’]).
‘” onclick=”document.getElementById(\’captcha\’).src=\’http://’.
$_SERVER[’HTTP_HOST’].”imagebuilder.php”.
‘; return false;”>Cant see it</a></p>’.”\n”.
‘<p><img id=”captcha” src=”imagebuilder.php” alt=”"></p>’.”\n”;

sorry i coun’t format the above code. just copy and paste it and everything should be fine.

Place a textbox on the form that accepts the cerification code:

that’s it, everything should work fine after that..

hope that this tutorial was informative and thank you for viewing

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PHP Contact form with image verification

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