Projects often encounter a series of security verification strategies such as login verification, payment verification and so on. There are various implementation methods. Let's explain how to use php to generate a simple text + number combination verification code:
The language used is php, gd library
Principle explanation:
a> In essence, the verification code is randomly generated on the server side and stored in $_SESSION.
b> Then write the verification code on the picture, send the picture to the client, and the user enters the verification code on the picture and submits it to the server.
c> The server compares with the information stored in $_SESSION, if it is consistent, it passes, otherwise it does not pass.
Divided into two steps:
1) The first step is to generate a verification code on the server side
2) The client uses the verification code
Step 1: How to generate a verification code on the server side: <code.php>
<?php
session_start(); //1>session_start() must be placed at the top, 2>multiple servers, consider centralized management of session information
//phpinfo();//Print out php information
//1. Generate a base map (width: 100; height: 30)
$image=imagecreatetruecolor(100,30);
$bgcolor=imagecolorallocate($image,255,255,255);//Brush coloring
imagefill($image,0,0,$bgcolor);//Color the basemap
// randomly generate four numbers
/*
for($i=0;$i<4;$i++){
$fontcolor=imagecolorallocate($image,rand(0,120),rand(0,120),rand(0,120));
$fontcontent=rand(0,9);//Content of verification code
$fontsize=6;//font size
$x=($i*100/4)+rand(5,10);//x axis
$y=rand(5,10);//Y轴
imagestring($image,$fontsize,$x,$y,$fontcontent,$fontcolor);//Use imagestring() to write text on the canvas
}
*/
$captch_code="";
for($i=0;$i<4;$i++){
$fontsize=6;
$fontcolor=imagecolorallocate($image,rand(20,100),rand(30,100),rand(10,200));
$str="abcdefghkmnpwsert1234567890";//Give a string to generate a random verification code
$fontcontent=substr($str,rand(0,strlen($str)),1);//Intercept one character at a time
$captch_code.=$fontcontent;//Splicing
$x=($i*100/4)+rand(5,10);
$y=rand(5,10);
imagestring($image,$fontsize,$x,$y,$fontcontent,$fontcolor);
}
$_SESSION['authcode']=$captch_code;//Save in session
//add distraction point
for($i=0;$i<100;$i++){
$pointcolor=imagecolorallocate($image,rand(50,200),rand(50,200),rand(50,200));
imagesetpixel($image,rand(0,100),rand(0,30),$pointcolor);
}
//Add interference line
for($i=0;$i<3;$i++){
$linecolor=imagecolorallocate($image,rand(80,200),rand(80,200),rand(80,200));
imageline($image,rand(5,95),rand(5,25),rand(5,95),rand(5,25),$linecolor);
}ob_clean();//Clear the cache
header("content-type:".'image/png');//The fixed format of the header file of the output image (can be image/jpg, image/png,)
imagepng($image);//Output an image to the browser
imagedestroy($image);//Destroy the basemap in memory
//session_start
Step 2: Return the generated verification code image to the client <form.php>
<?php
header("Content-type:text/html;charset=utf-8");//Avoid garbled characters
if(isset($_REQUEST['authcode'])){
session_start();//session_start() must be used before using $_SESSION
if(strtolower($_REQUEST['authcode'])==$_SESSION["authcode"]){//$_SESSION['authcode'] is the verification code stored on the server, $_REQUEST['authcode'] gets the client entered information
echo "<font color='#000cc'>The input is correct</font>";
}
else{
echo "<font color='#0000cc'>input error</font>";
}
exit();
}
?>
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Verification code is correct</title>
</head>
</html>
<body>
<form action="./form.php">
<p>Captcha image:<br>
//Click the verification code image itself to switch the verification code (requirement 1)
//Generate random numbers for easy access to the server, if the address is the same, the browser will not refresh the access
<img id="captCode" src="./code.php?=<?php echo rand();?>" width="100px;height:100px;" alt=""
onclick="this.src='code.php?+ Math.random()'">
//Click 'click to switch' to switch the verification code (requirement 2)
<img id="captCode" src="./code.php?=--><?php //echo rand();?><!--" width="100px;height:100px;" alt="">
<a href="javascript:void(0)" onclick="document.getElementById('captCode').src='code.php?=<?php echo rand();?>'">点击切换？</a>
</p>
<p>Please enter the content of the verification code:
<input type="text" name="authcode" value=""/>
</p>
<P>
<input type="submit" value="提交" style="padding:6px 20px;"/>
</P>
</form>
</body>
A few exceptions:
1): In case of garbled characters: header("Content-type:text/html;charset=utf-8");//Avoid garbled characters
2): If the captcha image cannot be displayed on the front end: it may be a cache problem:
Facts screenshot:
