How to achieve the effect of changing the verification code in PHP when the verification code cannot be seen clearly

php method to realize that the verification code cannot be seen and change one: first open the PHP code file; then add the js code "function changing(){document.getElementById('checkpic').src="/images/ ...}" to the page.

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Now let Let’s take a look at the PHP code

The code is as follows:

<?php
  
session_start();
function random($len) {
    $srcstr = "1a2s3d4f5g6hj8k9qwertyupzxcvbnm";
    mt_srand();
    $strs = "";
    for ($i = 0; $i < $len; $i++) {
        $strs .= $srcstr[mt_rand(0, 30)];
    }
    return $strs;
}
  
//随机生成的字符串
$str = random(4);
  
//验证码图片的宽度
$width  = 50;     
  
//验证码图片的高度
$height = 25;    
  
//声明需要创建的图层的图片格式
@ header("Content-Type:image/png");
  
//创建一个图层
$im = imagecreate($width, $height);
  
//背景色
$back = imagecolorallocate($im, 0xFF, 0xFF, 0xFF);
  
//模糊点颜色
$pix  = imagecolorallocate($im, 187, 230, 247);
  
//字体色
$font = imagecolorallocate($im, 41, 163, 238);
  
//绘模糊作用的点
mt_srand();
for ($i = 0; $i < 1000; $i++) {
    imagesetpixel($im, mt_rand(0, $width), mt_rand(0, $height), $pix);
}
  
//输出字符
imagestring($im, 5, 7, 5, $str, $font);
  
//输出矩形
imagerectangle($im, 0, 0, $width -1, $height -1, $font);
  
//输出图片
imagepng($im);
  
imagedestroy($im);
  
$str = md5($str);
  
//选择 cookie
//SetCookie("verification", $str, time() + 7200, "/");
  
//选择 Session
$_SESSION["verification"] = $str;
?>

Then just call it on the page:

The code is as follows:

<img id="checkpic" onclick="changing();" src=&#39;/images/checkcode.php&#39; />

If Want to achieve "can't see clearly?" Change "" effect, add the following JS to the page

The code is as follows:

function changing(){
    document.getElementById('checkpic').src="/images/checkcode.php?"+Math.random();
}

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