Captcha

Oct 222011

I built a captcha for a friend a while back for a shopping site, obviously it was too simple to be corrupted so I built this new one last night. It was not perfect though, as I don’t have enough knowledge to create dynamic fonts.

Under Ubuntu it is easy to get things work – install php5-gd, luckily it brought couple of fonts and then the script works like a charm. Under my friend’s machine I need to install some extra packages to get TrueType fonts, but it is not that hard.

Let’s see how this works, I believe the captcha is a little bit hard to be read, but it can block spammers.

2 Responses to “Captcha”

Hang says:

2011-10-22 at 19:03

Forgot to post code …

<?php
session_start();

$fonts = array(
    '/usr/share/fonts/truetype/ttf-dejavu/DejaVuSans.ttf',
    '/usr/share/fonts/truetype/ttf-dejavu/DejaVuSans-Bold.ttf',
    '/usr/share/fonts/truetype/ttf-dejavu/DejaVuSansMono.ttf',
    '/usr/share/fonts/truetype/ttf-dejavu/DejaVuSansMono-Bold.ttf',
    '/usr/share/fonts/truetype/ttf-dejavu/DejaVuSerif.ttf',
    '/usr/share/fonts/truetype/ttf-dejavu/DejaVuSerif-Bold.ttf',
);

$code = sprintf("%06d", rand(0,999999));
$weird = imagecreatetruecolor(160, 30);

$left = 5;
for ($index=0; $index<strlen($code); $index++) {
    $size = rand(15, 20); // sizes are between 10 and 20
    $angle = rand(0, 90) - 45; // angles are between -45 and 45 degrees
    $base_height = rand(20, 25); // bottom line of the character are between 20 and 25
    $color = imagecolorallocate($weird, rand(128,255), rand(128,255), rand(128,255)); // random color needs to be bright
    $font = $fonts[rand(0, count($fonts)-1)];
    $coords = imagettfbbox($size, $angle, $font, substr($code, $index, 1));
    $left -= min($coords[0], $coords[6]);
    imagettftext($weird, $size, $angle, $left, $base_height, $color, $font, substr($code, $index, 1));
    $left += max($coords[2], $coords[4]);
}

for ($index=0; $index<6; $index++) {
    imageline($weird,rand(0,160),rand(0,30),rand(0,160),rand(0,30),imagecolorallocate($weird, rand(128,255), rand(128,255), rand(128,255)));
}

$_SESSION['secret'] = md5($code);
header("Content-type: image/png");
imagepng($weird);
?>

Hang says:

2011-10-22 at 19:12

I need to find a good plugin for WordPress for better code posting, so far the codes look really ugly …

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