Somcaptcha

*** afbeelding.php ***
<?php
session_start();
header("Content-type: image/gif");
header("Expires: Wed, 1 Jan 1997 00:00:00 GMT");
header("Last-Modified: " . date("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");

//create image
$width = strlen($_SESSION['numberwork']) * 10;
$height = 18;
$image = imagecreate($width, $height);

//set white as transparant color
$backgroundcolor = imagecolorallocatealpha($image, 215, 215, 215, 127);
imagecolortransparent($image, $backgroundcolor);

//noise
for($i = 0; $i < 8; $i++) {
	$noiseColor = imagecolorallocate($image, rand(205, 255), rand(205, 255), rand(205, 255));
	$noiseX1 = rand(1, $width/2);
	$noiseY1 = rand(1, $height);
	$noiseX2 = rand($width/2, $width);
	$noiseY2 = rand(1, $height);
	imageline($image, $noiseX1, $noiseY1, $noiseX2, $noiseY2, $noiseColor);
	
	$text = rand(1,9);
	$fontsize = 12;
	$grey = rand(220, 255);
	$fontcolor = ImageColorAllocate($image, $grey, $grey, $grey);
	$font = 'fonts/GeosansLight.ttf';
	$angle = rand(-20,20);
	$x = rand(0, $width);
	$y = rand(0, $height);
	imagettftext($image, $fontsize, $angle, $x, $y, $fontcolor, $font, $text); 
}

//add text
$text = $_SESSION['numberwork'];
for($i = 0; $i <= strlen($text); $i++) {
	$character = substr($text, $i, 1);
	$fontsize = rand(12,16);
	$fontcolor = ImageColorAllocate($image, rand(0,100), rand(0,100), rand(0,100));
	$font = 'fonts/GeosansLight.ttf';
	$angle = rand(-10,10);
	if ($character == 'i' || $character == 'l') {
		$x = $i * 10.5;
	} else {
		$x = $i * 10;
	}
	$y = 14;
	imagettftext($image, $fontsize, $angle, $x, $y, $fontcolor, $font, $character); 
}

//clean up
imagegif($image);
imagedestroy($image);
?> 


*** voorbeeld.php ***
<?php
session_start();

if (isset($_POST['loginsum']) && $_POST['loginsum'] != "" && $_POST['loginsum'] == $_SESSION['loginsum']) {
	echo 'Correcte som';
}
if (isset($_POST['loginsum']) && $_POST['loginsum'] != "" && $_POST['loginsum'] != $_SESSION['loginsum']) {
	echo 'Foute som';
}

//numbers
$_NUMBERS = array();
$_NUMBERS[0] = "nul";
$_NUMBERS[1] = "een";
$_NUMBERS[2] = "twee";
$_NUMBERS[3] = "drie";
$_NUMBERS[4] = "vier";
$_NUMBERS[5] = "vijf";
$_NUMBERS[6] = "zes";
$_NUMBERS[7] = "zeven";
$_NUMBERS[8] = "acht";
$_NUMBERS[9] = "negen";
//calculations
$_CALCULATIONS = array();
$_CALCULATIONS[0] = "plus";
$_CALCULATIONS[1] = "min";

//generate random sum
$loginnumber1 = rand(0,9);
$loginnumber2 = rand(0,9);
$calculation = rand(0,1);
$_SESSION['numberwork'] = $_NUMBERS[$loginnumber1]." ".$_CALCULATIONS[$calculation]." ".$_NUMBERS[$loginnumber2];
if ($calculation == 0) {
	$sum = ($loginnumber1 + $loginnumber2);
} else {
	$sum = ($loginnumber1 - $loginnumber2);
}
$_SESSION['loginsum'] = $sum;

?>
<form id="captcha_test" method="post" action="" onsubmit="">
    <img src="afbeelding.php"> = <input name="loginsum" type="text" size="3" maxlength="3" /><br />
    <input type="submit" value="test" />    
</form>