Learn the simplest verification code production in php

The author is a computer student who is about to go out for an internship. PHP is purely my own hobby and I have learned some simple things by myself. Today I sent the verification code I made for everyone to give me some advice. Although it is simple, it took a lot of thought. The code is as follows:

<?php 
//定义图片格式
header("Content-type:image/png");

//定义画布大小，即验证码区域
$img=imagecreatetruecolor(80, 30);

//定义画笔颜色
$red1=imagecolorallocate($img, 0xff, 0x00, 0x00);
$green1=imagecolorallocate($img, 0x00, 0xff, 0x00);
$blue1=imagecolorallocate($img, 0x00, 0x00, 0xff);

//定义画布背景色
$bgcolor=imagecolorallocate($img, 0xff, 0xff, 0xff);

//将定义的颜色存入数组，以便随机换颜色
$col = array(&#39;0&#39; =>$red1,'1'=>$green1,'2'=>$blue1 );

//填充画布背景色
imagefill($img, 0, 0, $bgcolor);

//添加验证码内容
for($i=0;$i<4;$i++)
{
	$content .=&#39;&#39;; 
	$c
}
imagestring($img, 40, 20, 10, $content,$col[rand(0,2)] );


//添加干扰因素
	//添加干扰点
	for($i=0;$i<50;$i++)
	{
		imagesetpixel($img, rand(0,80), rand(0,40), $col[rand(0,2)]);
	}
	//添加干扰线
	for($j=0;$j<4;$j++)
	{	

		//imageline函数的格式：imageline(image, x1, y1, x2, y2, color)；
		imageline($img, rand(0,20), rand(0,20), rand(0,80), rand(0,30), $col[rand(0,2)]);
	}

//输出图像

imagepng($img);

//释放图像资源
imagedestroy($img);
?>



The above introduces the simplest verification code production for learning PHP, including the relevant content. I hope it will be helpful to friends who are interested in PHP tutorials.