php图片验证码

<?php
    header('Content-type:image/jpeg');
    $width=120;
    $height=40;
    $element=array('a','b','c','d','f','g','h','i','j','k','l','m','n');
    
    $img=  imagecreatetruecolor($width, $height);
    $colorBg=imagecolorallocate($img, rand(200,255),rand(200,255),rand(200,255));
    $colorBorder= imagecolorallocate($img, rand(200,255), rand(200,255), rand(200,255));
    $colorPixel=  imagecolorallocate($img, rand(100,200), rand(100,200), rand(100,200));
   $colorstring=  imagecolorallocate($img, rand(10,100), rand(10,100), rand(10,100));
    imagefill($img, 0, 0, $colorBg);
    imagerectangle($img, 0, 0, $width-1, $height-1, $colorBorder); 
    for($i=0;$i<100;$i++){
            imagesetpixel($img, rand(0,$width-1), rand(0, $height-1), $colorPixel);
    }
    for($i=0;$i<3;$i++){
        imageline($img, rand(0, $width/2), rand(0, $height), rand($width/2, $width), rand(0, $height), $colorPixel);
    }
//    imagestring($img,5, 0, 0, 'abcd', $colorPixel);
    for($i=0;$i<5;$i++){
        $string.=$element[rand(0, count($element)-1)];
    }
    imagettftext($img, 24, rand(-5, 5), rand(5,15), rand(30, 35), $colorstring, 'font/yugang.ttf', $string);
    imagejpeg($img);
    imagedestroy($img );
?>