A piece of code for php to generate dynamic image verification code

 session_start();
 function random($len)
 {
 $srCStr="ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
 $strs="";
 for($i=0;$i<$ len;$i++)
 {
 $strs.=$srCStr[mt_rand(0,35)];
 }
 return $strs;
 }
 $str=random(4); //Randomly generated string
 $ width = 50; //The width of the verification code image
 $height = 25; //The height of the verification code image
 @header("Content-Type:image/png");
 $_SESSION["code"] = $str ;
 $im = imagecreate($width,$height);
 //Background color
 $back = imagecolorallocate($im,0xFF,0xFF,0xFF);
 //Blurry point color
 $pix = imagecolorallocate($im, 187,230,247);
 //Font color
 $font = imagecolorallocate($im,41,163,238);
 //Points for blurring
 for($i=0;$i<1000;$i++)
 {
 imagesetpixel($ im,mt_rand(0,$width),mt_rand(0,$height),$pix);
 }
 imagestring($im, 5, 7, 5,$str, $font);
 imagerectangle($im,0 ,0,$width-1,$height-1,$font);
 imagepng($im);
 imagedestroy($im);
 $_SESSION["code"] = $str;
?>

Summary: Since PHP 4.2.0, you no longer need to use the srand() or mt_srand() function to seed the random number generator, it is now done automatically. Articles you may be interested in: php generates N non-repeating random numbers php randomly generates a 4-digit verification code php function to randomly display images php example of randomly displaying images Example of php generating random password PHP function to generate random username and password PHP program for batch generating random usernames Two ways to randomly generate Welfare Lottery numbers using php Function to generate random numbers using PHP Code to generate a random string using php Example of php generating random numbers php function to generate random string php random password generation function php function to generate random password PHP function to generate random string php function to generate random password Several ways to generate random passwords with php