How to implement verification code function in php

PHP implements the verification code function through the GD library, combined with examples to analyze the PHP verification code related image drawing and output operation implementation techniques. Share it with everyone for your reference, the details are as follows:

First look at the effect achieved: (recommended learning: PHP video Tutorial)

Specific implementation:

<?php
/*PHP实现验证码*/
session_start();//开启会话
//创建画布
$image=imagecreatetruecolor(100,38);
//背景颜色
$bgcolor=imagecolorallocate($image,255,255,255);
imagefill($image,0,0,$bgcolor);
$captch_code=&#39;&#39;;//存储验证码
//随机选取4个数字
for($i=0;$i<4;$i++){
  $fontsize=10;    //
  $fontcolor=imagecolorallocate($image,rand(0,120),rand(0,120),rand(0,120));//随机颜色
  $fontcontent=rand(0,9);
  $captch_code.=$fontcontent;
  $x=($i*100/4)+rand(5,10);  //随机坐标
  $y=rand(5,10);
  imagestring($image,$fontsize,$x,$y,$fontcontent,$fontcolor);
}
/*//字母和数字混合验证码
for($i=0;$i<4;$i++) {
  $fontsize = 10;    //
  $fontcolor = imagecolorallocate($image, rand(0, 120), rand(0, 120), rand(0, 120));//??????
  $data = &#39;abcdefghijklmnopqrstuvwxyz1234567890&#39;;  //数据字典
  $fontcontent = substr($data, rand(0, strlen($data)), 1);
  $captch_code.=$fontcontent;
  $x = ($i * 100 / 4) + rand(5, 10);
  $y = rand(5, 10);
  imagestring($image, $fontsize, $x, $y, $fontcontent, $fontcolor);
}*/
$_SESSION[&#39;code&#39;]=$captch_code;
//增加干扰点
for($i=0;$i<200;$i++){
  $pointcolor=imagecolorallocate($image,rand(50,200),rand(50,200),rand(50,200));
  imagesetpixel($image,rand(1,99),rand(1,29),$pointcolor);//
}
//增加干扰线
for($i=0;$i<3;$i++){
  $linecolor=imagecolorallocate($image,rand(80,280),rand(80,220),rand(80,220));
  imageline($image,rand(1,99),rand(1,29),rand(1,99),rand(1,29),$linecolor);
}
//输出格式
header(&#39;content-type:image.png&#39;);
imagepng($image);
//销毁图片
imagedestroy($image);

To realize the connection of forms and the "change one" function Implementation:

<input type="text" placeholder="验证码" name="verifycode" class="captcha">
<br>
<img  id="captcha_img" src="captcha.php?r=<?php echo rand();? alt="How to implement verification code function in php" >" alt="验证码">
<label>
<a href="javascript:void(0)" rel="external nofollow" onclick="document.getElementById(&#39;captcha_img&#39;).src=&#39;captcha.php?r=&#39;+Math.random()">换一个</a> 
</label>

captcha.php is followed by a random parameter to achieve the function of changing a verification code. Changing the function can be achieved through simple js. If there is no such function, no parameters can be used.

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