Summary of methods for generating various random verification codes in PHP

This article mainly introduces the methods for PHP to generate various random verification codes. It summarizes and analyzes the commonly used techniques for generating verification codes in PHP based on specific examples. It also comes with demo source code for readers to download and refer to. Friends who need it can refer to it. The following

examples in this article summarize the methods of generating various random verification codes in PHP. Share it with everyone for your reference, the details are as follows:

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

Click here to download the sample source code from this site.

PHP generates a verification code image

The principle of PHP generating verification code: Use PHP's GD library to generate a picture with a verification code , 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 image;

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.

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
}

getCode() to explain 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 some pixels

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

imagedestroy(): Release the memory occupied by the image

Ajax refresh and verification

<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"></p>
<p><input type="button" class="btn" id="chk_num" value="提交" /></p>

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

$(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！");
      }
    });
  });
});

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

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