PHP verification code function code (simple and practical)_PHP tutorial

/**
* vCode(m,n,x,y) m numbers, display size is n, side width x, side height y
* micxp
*jb51.net
*/
session_start();
vCode(4, 15); //4 numbers, display size is 15

function vCode($num = 4, $size = 20, $width = 0, $height = 0) {
!$width && $width = $num * $size * 4 / 5 + 5;
!$height && $height = $size + 10; // Remove 0 1 O L and other
$ Str = "23456789abcdefghijkmnpqrstuvwxyzabcdeFghijklmnpqrstuvw";
$ code = ''; & lt; $ num ; $i++) {
$code .= $str[mt_rand(0, strlen($str)-1)];
} // Draw an image
$im = imagecreatetruecolor($width , $height);
// Define the color to be used
$back_color = imagecolorallocate($im, 235, 236, 237);
$boer_color = imagecolorallocate($im, 118, 151, 199 );
$text_color = imagecolorallocate($im, mt_rand(0, 200), mt_rand(0, 120), mt_rand(0, 120));
// Draw background
imagefilledrectangle($im, 0, 0, $width, $height, $back_color);
// Draw a border
imagerectangle($im, 0, 0, $width-1, $height-1, $boer_color);
// Draw interference lines
for($i = 0;$i < 5;$i++) {
$font_color = imagecolorallocate($im, mt_rand(0, 255), mt_rand(0, 255), mt_rand(0, 255));
imagearc($im, mt_rand(- $width, $width), mt_rand(- $height, $height), mt_rand(30, $width * 2), mt_rand(20, $height * 2), mt_rand(0, 360), mt_rand(0, 360), $font_color);
} }
// Draw interference points
for($i = 0;$i < 50;$i++) {
$font_color = imagecolorallocate($im, mt_rand(0, 255), mt_rand(0, 255), mt_rand(0, 255));
imagesetpixel($im, mt_rand(0) , $width), mt_rand(0, $height), $font_color);
} }
// Draw verification code
@imagefttext($im, $size , 0, 5, $size + 3, $text_color, 'c:\WINDOWS\Fonts\simsun.ttc', $code);
$_SESSION["VerifyCode"]=$code;
header("Cache-Control: max-age=1, s-maxage=1, no-cache, must-revalidate");
header("Content-type: image/png;charset=gb2312");
imagepng($im);
imagedestroy( $im);
}
?>