Detailed explanation of php random verification code image generation example

/**Default homepage **/
class DefaultController extends AppController
{
public function index() {
$len = 5;
$str = "ABCDEFGHIJKLNMPQRSTUVWXYZ12 3456789" ;
$im = imagecreatetruecolor ( 70, 20 );
$bgc = imagecolorallocate($im, 255, 255, 255);
$bgtxt = imagecolorallocate($im, 220, 220, 220);
//Random palette
$colors = array(
imagecolorallocate($im, 255, 0, 0),
imagecolorallocate($im, 0, 200, 0) ,
imagecolorallocate($im, 0, 0, 255),
imagecolorallocate($im, 0, 0, 0),
imagecolorallocate($im, 255, 128, 0),
imagecolorallocate($im, 255, 208, 0),
imagecolorallocate($im, 98, 186, 245),
);
//Fill the background color
imagefill($im, 0, 0, $bgc);< /p>
//Get random numbers
$verify = "";
while (strlen($verify) < $len) {
$i = strlen($verify);
$random = $str [rand(0, strlen($str))];
$verify .= $random;
//Draw background text
imagestring($im, 6, ($i*10) +3, rand(0,6), $random, $bgtxt);
//Draw the main text information
imagestring($im, 6, ($i*10)+3, rand(0,6), $random , $colors[rand(0, count($colors)-1)]);
}
//Add random noise
for($i=0; $i<100; $i++) {
$color = imagecolorallocate($im, rand(50,220), rand(50,220), rand(50,220));
imagesetpixel($im, rand(0,70), rand(0,20), $ color);
}
//Save the verification code in $_SESSION
sess("verify", $verify);
//Output picture And release the cache
header('Content-type: image/png');
imagepng($im);
imagedestroy($im);
}
};
?>

Example 2, PHP instance of a class that generates random strings and verification codes Class for generating random strings and verification codes.

The implementation of the following code is mainly to distinguish one get_code() and the other create_check_image(). The output image directly calls the latter one. When session() takes the verification code, just get_code() directly. When using session, session_star() must be placed first.

Full code:

class RandCheckCode
{
 /*Function name: get_code()
 *Function: Get a random string
 *Parameters:
 1. (int)$length = 32 #Random character length
 2. (int)$mode = 0 #Random character type,
 0 is uppercase and lowercase English and numbers, 1 is numbers, 2 is lowercase letters, 3 is uppercase letters,
 4 is uppercase and lowercase letters, 5 is uppercase letters and numbers, 6 is lowercase letters and numbers
 *Return: obtained string
 */
 function get_code($length=32,$mode=0)//Get random verification code function
 {
 switch ( $mode)
 {
 case '1':
 $str='123456789';
 break;
 case '2':
 $str='abcdefghijklmnopqrstuvwxyz';
 break;
 case '3':
 $str=' ABCDEFGHIJKLMNOPQRSTUVWXYZ';
 break;
 case '4':
 $str='ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz';
 break;
 case '5':
 $str='ABCDEFGHIJKLMNOPQRSTUVWXYZ12345678 90';
 break;
 case '6':
 $str= 'abcdefghijklmnopqrstuvwxyz1234567890';
 break;
 default:
 $str='ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz1234567890';
 break;
 }
 $checkstr='';
 $len =strlen($str)-1;
 for ($i=0; $i<$length;$i++)
 {
 //$num=rand(0,$len);//Generate a random number between 0 and $len
 $num=mt_rand(0,$len); //Generate a random number between 0 and $len
 $checkstr.=$str[$num];

 }
 return $checkstr;
 }
 /**Function name: create_check_image()
 Function: Generate a check code image
 Parameters: $checkcode: Verification code string
 Return value: Return the image
*/
 function create_check_image($checkcode)//Generate a
 {
 $im=imagecreate(65,22);//Generate an image
 $black=imagecolorallocate($im, 0,0,0);//Background color
 $white=imagecolorallocate($im,255,255,255);//Foreground color
 $gray=imagecolorallocate($im,200,200,200);
 imagefill($im,30,30,$ gray); //Perform area filling with $gray color at coordinates 30,30 of the $im image (the upper left corner of the image is 0,0) (that is, points with the same color and adjacent points at 30,30 will be filled)< ;/p>
 imagestring($im,5,8,3,$checkcode,$white);//Use $white color to draw the string $checkcode to 8,3 of the image represented by $im coordinates (this is the coordinate of the upper left corner of the string, the upper left corner of the entire image is 0,0), 5 is the font size, the font can only be 1, 2, 3, 4 or 5, use the built-in font
 for ($i =0;$i<120;$i++)
 {
 $randcolor=imagecolorallocate($im,rand(0,255),rand(0,255),rand(0,255));
 imagesetpixel($im,rand()%70, rand()%30,$randcolor);//Use $randcolor color to draw a point on the $im image at (rand()%70, rand()%30) coordinates (the upper left corner of the image is 0,0)
 }
 header("Content-type:image/png");
 imagepng($im);//Output the image to the browser or file in PNG format
 imagedestroy($im);//Destroy the image $im
 }
}
/*
$randcode=new RandCheckCode();
$checkstring=$randcode->get_code(5,7);
$image=$randcode->create_check_image($checkstring);
echo $image ;
*/
?>