Version: 1.0
Type: Full Script
Category: Graphics
License: GNU General Public License
Description: Quick snippet I put together to display random numbers in an image on a form. The user types the numbers he/she sees into an input box on the form to validate that it is a human filling out the form and not a bot.
Numbers are random by font, size, and position in the graphic. Size of the graphic and number of digits are easily controlled to your liking. The numeric representation of the image numbers is not stored in the form, so bots can not get at it to circumvent your security.
There are two snipets here. The first, “send_imagever.php” generates the graphic and stores a hash of the real number in a session variable. The second, “stub_imgver.php” is quick stub to demonstrate the use of the code.
<?PHP
/////////////////////////////////////////////
// send_imagever.php //
/////////////////////////////////////////////
session_start();
// set up some default values
// ~~~~~~~~~~~~~~~~~~~~~~~~~~
$sessionvar = 'imageVerHash';
$imgWidth = 96;
$imgHeight = 36;
$borderThick = 1;
$numChars = 5;
// set up blank image pallet with borders
// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
$image = imagecreate($imgWidth, $imgHeight);
$bgColor = imagecolorallocate ($image, 255, 255, 255);
$textColor = imagecolorallocate ($image, 0, 0, 0);
// Initialize some values
// ~~~~~~~~~~~~~~~~~~~~~~
$numString = ''; // init string of numbers
$minX = $borderThick +2; // first x position for chars
$minY = $borderThick +2; // lowest y position for chars
srand(make_seed()); // seed the random generator
// Loop $numChars times, generate random char/font/offset
// and render to image object
// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
$idx = 0;
while ($idx < $numChars):
// pick a font and calculate the character size for it
$font = rand(3,5); // pick a font (3,4,or5)
$fontWidth = imagefontwidth($font);
$fontHeight = imagefontheight($font);
// pick a random digit and add it to the string
if ($font > 4) {
$char = rand(0,9); // small zeroes are confusing
} // because they look like 8's
else { // so avoid them
$char = rand(1,9);
}
$numString .= $char;
$xOffset = $minX + rand(3,10); // pick new x offset
$minX = $xOffset + $fontWidth; // new minX is right side of new char
// pick a random Y offset (within available space)
$maxY = $imgHeight - $borderThick - $fontHeight;
$yOffset = rand($minY, $maxY);
// render the character to the image
imagechar ($image, $font, $xOffset, $yOffset, $char, $textColor);
$idx++;
endwhile;
// draw border;
if ($borderThick > 0) {
imagelinethick ($image, 1,1,$imgWidth,1,$textColor,$borderThick);
imagelinethick ($image, 1,1,1,$imgHeight,$textColor,$borderThick);
imagelinethick ($image, $imgWidth-$borderThick,1,$imgWidth-$borderThick,$imgHeight,$textColor,$borderThick);
imagelinethick ($image, 1,$imgHeight-$borderThick,$imgWidth,$imgHeight-$borderThick,$textColor,$borderThick);
}
// save hash of string in session var
// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
$_SESSION[$sessionvar] = md5($numString);
// Send out enough headers so the image is NEVER cached by browsers
// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
header("Expires: Mon, 26 Jul 1997 05:00:00 GMT");
header("Last-Modified: " . gmdate("D, d M Y H:i:s") . " GMT");
header("Cache-Control: no-store, no-cache, must-revalidate");
header("Cache-Control: post-check=0, pre-check=0", false);
header("Pragma: no-cache");
// Send the image to the browser
// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
header('Content-type: image/jpeg');
imagejpeg($image);
imagedestroy($image);
return;
///////////////////////////////////////////////////////////////////////
// This is just a fancy function to draw the borders //
///////////////////////////////////////////////////////////////////////
function imagelinethick($image, $x1, $y1, $x2, $y2, $color, $thick = 1)
{
if ($thick == 1) {
return imageline($image, $x1, $y1, $x2, $y2, $color);
}
$t = $thick / 2 - 0.5;
if ($x1 == $x2 || $y1 == $y2) {
return imagefilledrectangle($image, round(min($x1, $x2) - $t), round(min($y1, $y2) - $t), round(max($x1, $x2) + $t), round(max($y1, $y2) + $t), $color);
}
$k = ($y2 - $y1) / ($x2 - $x1); //y = kx + q
$a = $t / sqrt(1 + pow($k, 2));
$points = array(
round($x1 - (1+$k)*$a), round($y1 + (1-$k)*$a),
round($x1 - (1-$k)*$a), round($y1 - (1+$k)*$a),
round($x2 + (1+$k)*$a), round($y2 - (1-$k)*$a),
round($x2 + (1-$k)*$a), round($y2 + (1+$k)*$a),
);
imagefilledpolygon($image, $points, 4, $color);
return imagepolygon($image, $points, 4, $color);
}
?>
<?PHP
/////////////////////////////////////////////
// stub_imgver.php //
/////////////////////////////////////////////
session_start();
if ( isset($_POST['submit']) &&
isset($_POST['imagever']) &&
isset($_SESSION['imageVerHash'])
) {
$verstring = trim($_POST['imagever']);
$formhash = md5($verstring);
if ($formhash == trim($_SESSION['imageVerHash'])) {
print "matched";
unset($_SESSION['imageVerHash']);
}
else {
unset($_SESSION['imageVerHash']);
print "no match";
}
}
else {
print "
<html>
<head>
<title>Image Verification Stub</title>
</head>
<body>
<FORM ACTION="" . $_SERVER['PHP_SELF'] . "" NAME="myform" METHOD="POST" ENCTYPE="application/x-www-form-urlencoded">
<input type="text" name="imagever"><img src="send_imagever.php">
<input type="submit" name="submit" value="SUBMIT">
</form>
</body>
</html>
";
}
?>
