How to randomly generate verification code in php

Verification code is very important in WEB applications. It is usually used to prevent users from maliciously submitting forms, such as malicious registration and login, malicious forum spamming, etc. This article will use examples to explain the use of PHP to generate various common verification codes, including digital verification codes, alphanumeric verification codes, Chinese verification codes, arithmetic verification codes, etc., as well as the Ajax verification process.

PHP generates verification code image

The principle of PHP generating verification code: Use PHP's GD library to generate a verification code code picture and save the verification code in Session. The general process of generating verification code by PHP is:

1. Generate a png picture;

2. Set the background color for the picture;

3. Set the font color and Style;

4. Generate a 4-digit random verification code;

5. Adjust the rotation angle and position of each generated character and draw it on the png picture;

6. Add noise and interference lines to prevent the registration machine from analyzing the original image to maliciously crack the verification code;

7. Output the image;

8. Release the memory occupied by the image.

Related recommendations: "php Getting Started Tutorial"

Sample code:

session_start();
getCode(4,60,20);
function getCode($num,$w,$h) {
  $code = "";
  for ($i = 0; $i < $num; $i++) {
    $code .= rand(0, 9);
  }
  //4位验证码也可以用rand(1000,9999)直接生成
  //将生成的验证码写入session，备验证时用
  $_SESSION["helloweba_num"] = $code;
  //创建图片，定义颜色值
  header("Content-type: image/PNG");
  $im = imagecreate($w, $h);
  $black = imagecolorallocate($im, 0, 0, 0);
  $gray = imagecolorallocate($im, 200, 200, 200);
  $bgcolor = imagecolorallocate($im, 255, 255, 255);
  //填充背景
  imagefill($im, 0, 0, $gray);
  //画边框
  imagerectangle($im, 0, 0, $w-1, $h-1, $black);
  //随机绘制两条虚线，起干扰作用
  $style = array ($black,$black,$black,$black,$black,
    $gray,$gray,$gray,$gray,$gray
  );
  imagesetstyle($im, $style);
  $y1 = rand(0, $h);
  $y2 = rand(0, $h);
  $y3 = rand(0, $h);
  $y4 = rand(0, $h);
  imageline($im, 0, $y1, $w, $y3, IMG_COLOR_STYLED);
  imageline($im, 0, $y2, $w, $y4, IMG_COLOR_STYLED);
  //在画布上随机生成大量黑点，起干扰作用;
  for ($i = 0; $i < 80; $i++) {
    imagesetpixel($im, rand(0, $w), rand(0, $h), $black);
  }
  //将数字随机显示在画布上,字符的水平间距和位置都按一定波动范围随机生成
  $strx = rand(3, 8);
  for ($i = 0; $i < $num; $i++) {
    $strpos = rand(1, 6);
    imagestring($im, 5, $strx, $strpos, substr($code, $i, 1), $black);
    $strx += rand(8, 12);
  }
  imagepng($im);//输出图片
  imagedestroy($im);//释放图片所占内存
}

Custom function getCode() in the code Explains the verification code generation process. Using the image processing functions that come with the PHP GD library, you can easily generate various desired picture effects.

·imagecreate(): Create a new image

·imagecolorallocate(): Assign a color to the image

·imagefill(): Fill the image

·imagerectangle(): Draw a rectangle (border)

·imagesetstyle() ：Set the line drawing style

·imageline()：Draw a line segment

·imagesetpixel()：Draw pixels

·imagepng(): Output the image to the browser or file in PNG format

·imagedestroy(): Release the memory occupied by the image

Save the above code as code_num.php for easy calling.

Ajax refresh and verification

After the verification code is generated, we need to apply it in the actual project. Usually we use ajax to refresh and generate a new verification code when clicking on it. Verification code (sometimes the generated verification code is difficult to identify with the naked eye), that is, "change another one if you can't see it clearly". After filling in the verification code, you also need to verify whether the verification code is correct. The verification process is completed by a background program, but we can also achieve refresh-free verification through ajax.

We create a front-end page index.html, load jQuery, and add the verification code form element to the body:

<p>验证码：<input type="text" class="input" id="code_num" name="code_num" maxlength="4" />
<img  src="code_num.php" id="getcode_num" title="看不清，点击换一张" align="absmiddle" alt="How to randomly generate verification code in php" ></p>
<p><input type="button" class="btn" id="chk_num" value="提交" /></p>

In the html code,

$(function(){
  //数字验证
  $("#getcode_num").click(function(){
    $(this).attr("src",'code_num.php?' + Math.random());
  });
  ...
});

Refreshing the verification code actually means re-requesting the verification code generation program. What should be noted here is calling code_num. PHP should bring random parameters to prevent caching. Next, after filling in the verification code, click the "Submit" button, and through $.post(), the front end sends an ajax request to the background chk_code.php.

$(function(){
  ...
  $("#chk_num").click(function(){
    var code_num = $("#code_num").val();
    $.post("chk_code.php?act=num",{code:code_num},function(msg){
      if(msg==1){
        alert("验证码正确！");
      }else{
        alert("验证码错误！");
      }
    });
  });
});

Backend chk_code.php verification:

session_start();
$code = trim($_POST['code']);
if($code==$_SESSION["helloweba_num"]){
  echo '1';
}

The background completes the verification based on comparing the submitted verification code with the verification code saved in the session.

For the generation and use of other verifications, the principle is the same. Developers can generate multiple styles of random verification codes as needed. The demo of this article provides numerical verification codes, alphanumeric verification codes, Chinese verification code, imitation Google verification code, arithmetic verification code, etc.

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