function _code($_code_length = 4, $_width = 75, $_height = 25){     for($i=0;$i<$_code_length;$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 < 6; $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 < 50; $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 < $_code_length ; $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); }