HKCaptcha: PHP Source code
Image generation algorithm
Contents of captcha-image.php.
<?php
/***************************************
Han-Kwang Nienhuys' PHP captcha
Copyright June 2007
This copyright message and attribution must be preserved upon
modification. Redistribution under other licenses is expressly allowed.
Other licenses include GPL 2 or higher, BSD, and non-free licenses.
The original, unrestricted version can be obtained from
http://www.lagom.nl/linux/hkcaptcha/ .
**************************************
Yet another captcha implementation in PHP. This one is written with
the current state (as of 2007) of captcha-defeating research in
mind. Apart from a letter distortion that is more advanced than just
rotating the letters, the clutter is designed to make segmentation of
the image into separate letter glyphs hard to do automatically.
The 5-letter code is stored into the PHP session variable
$_SESSION['captcha_string']; see the examples example.html and verify.php.
***************************************/
// CONFIG
$font = "include/VeraSeBd.ttf";
$signature = "www.lagom.nl";
$perturbation = 1.0; // bigger numbers give more distortion; 1 is standard
$imgwid = 200; // image width, pixels
$imghgt = 100; // image height, pixels
$numcirc = 4; // number of wobbly circles
$numlines = 3; // number of lines
// END CONFIG
// global vars
$ncols = 20; // foreground or background cols
// end global vars
function frand()
{
return 0.0001*rand(0,9999);
}
// wiggly random line centered at specified coordinates
function randomline($img, $col, $x, $y)
{
$theta = (frand()-0.5)*M_PI*0.7;
global $imgwid;
$len = rand($imgwid*0.4,$imgwid*0.7);
$lwid = rand(0,2);
$k = frand()*0.6+0.2; $k = $k*$k*0.5;
$phi = frand()*6.28;
$step = 0.5;
$dx = $step*cos($theta);
$dy = $step*sin($theta);
$n = $len/$step;
$amp = 1.5*frand()/($k+5.0/$len);
$x0 = $x - 0.5*$len*cos($theta);
$y0 = $y - 0.5*$len*sin($theta);
$ldx = round(-$dy*$lwid);
$ldy = round($dx*$lwid);
for ($i = 0; $i < $n; ++$i) {
$x = $x0+$i*$dx + $amp*$dy*sin($k*$i*$step+$phi);
$y = $y0+$i*$dy - $amp*$dx*sin($k*$i*$step+$phi);
imagefilledrectangle($img, $x, $y, $x+$lwid, $y+$lwid, $col);
}
}
// amp = amplitude (<1), num=numwobb (<1)
function imagewobblecircle($img, $xc, $yc, $r, $wid, $amp, $num, $col)
{
$dphi = 1;
if ($r > 0)
$dphi = 1/(6.28*$r);
$woffs = rand(0,100)*0.06283;
for ($phi = 0; $phi < 6.3; $phi += $dphi) {
$r1 = $r * (1-$amp*(0.5+0.5*sin($phi*$num+$woffs)));
$x = $xc + $r1*cos($phi);
$y = $yc + $r1*sin($phi);
imagefilledrectangle($img, $x, $y, $x+$wid, $y+$wid, $col);
}
}
// make a distorted copy from $tmpimg to $img. $wid,$height apply to $img,
// $tmpimg is a factor $iscale bigger.
function distorted_copy($tmpimg, $img, $width, $height, $iscale)
{
$numpoles = 3;
// make an array of poles AKA attractor points
global $perturbation;
for ($i = 0; $i < $numpoles; ++$i) {
do {
$px[$i] = rand(0, $width);
} while ($px[$i] >= $width*0.3 && $px[$i] <= $width*0.7);
do {
$py[$i] = rand(0, $height);
} while ($py[$i] >= $height*0.3 && $py[$i] <= $height*0.7);
$rad[$i] = rand($width*0.4, $width*0.8);
$tmp = -frand()*0.15-0.15;
$amp[$i] = $perturbation * $tmp;
}
// get img properties bgcolor
$bgcol = imagecolorat($tmpimg, 1, 1);
$width2 = $iscale*$width;
$height2 = $iscale*$height;
// loop over $img pixels, take pixels from $tmpimg with distortion field
for ($ix = 0; $ix < $width; ++$ix)
for ($iy = 0; $iy < $height; ++$iy) {
$x = $ix;
$y = $iy;
for ($i = 0; $i < $numpoles; ++$i) {
$dx = $ix - $px[$i];
$dy = $iy - $py[$i];
if ($dx == 0 && $dy == 0)
continue;
$r = sqrt($dx*$dx + $dy*$dy);
if ($r > $rad[$i])
continue;
$rscale = $amp[$i] * sin(3.14*$r/$rad[$i]);
$x += $dx*$rscale;
$y += $dy*$rscale;
}
$c = $bgcol;
$x *= $iscale;
$y *= $iscale;
if ($x >= 0 && $x < $width2 && $y >= 0 && $y < $height2)
$c = imagecolorat($tmpimg, $x, $y);
imagesetpixel($img, $ix, $iy, $c);
}
}
// add grid for debugging purposes
function addgrid($tmpimg, $width2, $height2, $iscale, $color) {
$lwid = floor($iscale*3/2);
imagesetthickness($tmpimg, $lwid);
for ($x = 4; $x < $width2-$lwid; $x+=$lwid*2)
imageline($tmpimg, $x, 0, $x, $height2-1, $color);
for ($y = 4; $y < $height2-$lwid; $y+=$lwid*2)
imageline($tmpimg, 0, $y, $width2-1, $y, $color);
}
function warped_text_image($width, $height, $string)
{
// internal variablesinternal scale factor for antialias
$iscale = 3;
// initialize temporary image
$width2 = $iscale*$width;
$height2 = $iscale*$height;
$tmpimg = imagecreate($width2, $height2);
$bgColor = imagecolorallocatealpha ($tmpimg, 192, 192, 192, 100);
$col = imagecolorallocate($tmpimg, 0, 0, 0);
// init final image
$img = imagecreate($width, $height);
imagepalettecopy($img, $tmpimg);
imagecopy($img, $tmpimg, 0,0 ,0,0, $width, $height);
// put straight text into $tmpimage
global $font;
$fsize = $height2*0.25;
$bb = imageftbbox($fsize, 0, $font, $string);
$tx = $bb[4]-$bb[0];
$ty = $bb[5]-$bb[1];
$x = floor($width2/2 - $tx/2 - $bb[0]);
$y = round($height2/2 - $ty/2 - $bb[1]);
imagettftext($tmpimg, $fsize, 0, $x, $y, -$col, $font, $string);
// addgrid($tmpimg, $width2, $height2, $iscale, $col); // debug
// warp text from $tmpimg into $img
distorted_copy($tmpimg, $img, $width, $height, $iscale);
// add wobbly circles (spaced)
global $numcirc;
for ($i = 0; $i < $numcirc; ++$i) {
$x = $width * (1+$i) / ($numcirc+1);
$x += (0.5-frand())*$width/$numcirc;
$y = rand($height*0.1, $height*0.9);
$r = frand();
$r = ($r*$r+0.2)*$height*0.2;
$lwid = rand(0,2);
$wobnum = rand(1,4);
$wobamp = frand()*$height*0.01/($wobnum+1);
imagewobblecircle($img, $x, $y, $r, $lwid, $wobamp, $wobnum, $col);
}
// add wiggly lines
global $numlines;
for ($i = 0; $i < $numlines; ++$i) {
$x = $width * (1+$i) / ($numlines+1);
$x += (0.5-frand())*$width/$numlines;
$y = rand($height*0.1, $height*0.9);
randomline($img, $col, $x, $y);
}
return $img;
}
function add_text($img, $string)
{
$cmtcol = imagecolorallocatealpha ($img, 128, 0, 0, 64);
imagestring($img, 5, 10, imagesy($img)-20, $string, $cmtcol);
}
// start main program
session_start();
// generate 5 letter random string
$rand = "";
// some easy-to-confuse letters taken out C/G I/l Q/O h/b
$letters = "ABDEFHKLMNOPRSTUVWXZabdefghikmnopqrstuvwxyz";
for ($i = 0; $i < 5; ++$i) {
$rand .= substr($letters, rand(0,strlen($letters)-1), 1);
}
// create the hash for the random number and put it in the session
$_SESSION['captcha_string'] = $rand;
$image = warped_text_image($imgwid, $imghgt, $rand);
add_text($image, $signature);
// send several headers to make sure the image is not cached
// taken directly from the PHP Manual
// Date in the past
header("Expires: Mon, 26 Jul 1997 05:00:00 GMT");
header("Last-Modified: " . gmdate("D, d M Y H:i:s") . " GMT");
header("Cache-Control: no-store, no-cache, must-revalidate");
header("Cache-Control: post-check=0, pre-check=0", false);
header("Pragma: no-cache");
header('Content-type: image/png');
// send the image to the browser
imagepng($image);
// destroy the image to free up the memory
imagedestroy($image);
?>
Verification script
Contents of example verify.php.
<?php
session_start();
// check captcha post form field, return 1 if OK
// it is case-insensitive.
function check_captcha()
{
if (!isset($_POST['captcha']))
return 0;
$userletters = strtoupper($_POST['captcha']);
if (!isset($_SESSION['captcha_string']))
return 0;
if ($userletters === strtoupper($_SESSION['captcha_string'])) {
// make sure that the code is only used once
unset($_SESSION['captcha_string']);
return 1;
}
return 0;
}
?>
<html>
<body>
Captcha test: <?php print check_captcha() ? "PASSED" : "FAILED"; ?>
</body>
<html>
