一个简单php验证码程序代码

function _code($_code_length = 4, $_width = 75, $_height = 25){
for($i=0;$i $_nmsg .= dechex(mt_rand(0,15));
}
$_SESSION["code"] = $_nmsg;

$_img = imagecreatetruecolor($_width, $_height);

$_white = imagecolorallocate($_img, 250, 250, 250);

imagefill($_img, 0, 0, $_white);

$_gray = imagecolorallocate($_img, 196, 196, 196);

imagerectangle($_img, 0, 0, $_width-1, $_height-1, $_gray);

for ($i=0; $i $_md_color = imagecolorallocate($_img, mt_rand(200,255), mt_rand(200,255), mt_rand(200,255));
imageline($_img, mt_rand(0,$_width), mt_rand(0, $_height),mt_rand(0,$_width), mt_rand(0, $_height), $_md_color);
}

for ($i=0; $i $_md_color = imagecolorallocate($_img, mt_rand(200,255), mt_rand(200,255), mt_rand(200,255));
imagestring($_img, 1, mt_rand(1,$_width-5), mt_rand(1, $_height-5), "*", $_md_color);
}

for ($i=0; $i $_md_color = imagecolorallocate($_img, mt_rand(0,102), mt_rand(0,102), mt_rand(0,102));
imagestring($_img, 5, $i * $_width/$_code_length+ mt_rand(1, 10), mt_rand(1, $_height/2), $_SESSION["code"][$i], $_md_color);
}

header("Content-Type:image/png");

imagepng($_img);

imagedestroy($_img);
}

$getcode = $_POST['code'];

if( $_SESSION["code"] = $getcode )
{
echo ' 验证合法，进入下一步';
unset( $_SESSION["code"] );
}
else
{
echo ' 验证码不正确';
header('location:vial.php');
}