What is a verification code?
Verification code is to generate a picture from a string of randomly generated numbers or symbols, with some interfering pixels added to the picture (to prevent OCR), and the verification code is visually recognized by the user. Code information, enter the form and submit for website verification. A certain function can only be used after successful verification.
The function of the verification code:
Effectively prevent a hacker from continuously logging in to a specific registered user using a specific program to brute force try. In fact, modern verification codes generally prevent machines from registering in batches and preventing machines from posting replies in batches. Currently, many websites use verification code technology to prevent users from using robots to automatically register, log in, and spam.
What we are mainly talking about here is the random digital picture verification code. The characters on the pictures are relatively regular, some may have some random interferon added, and some have random character colors.
Publish a basic image that generates a png picture verification code:
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 registration machine analysis Original picture to maliciously register
7, output picture
8, release the memory occupied by the picture
The following is an example of PHP verification code code:
<?php
//设置session,必须处于脚本最顶部
session_start();
$image = imagecreatetruecolor(100, 30); //1>设置验证码图片大小的函数
//5>设置验证码颜色 imagecolorallocate(int im, int red, int green, int blue);
$bgcolor = imagecolorallocate($image,255,255,255); //#ffffff
//6>区域填充 int imagefill(int im, int x, int y, int col) (x,y) 所在的区域着色,col 表示欲涂上的颜色
imagefill($image, 0, 0, $bgcolor);
//10>设置变量
$captcha_code = "";
//7>生成随机数字
for($i=0;$i<4;$i++){
//设置字体大小
$fontsize = 6;
//设置字体颜色，随机颜色
$fontcolor = imagecolorallocate($image, rand(0,120),rand(0,120), rand(0,120)); //0-120深颜色
//设置数字
$fontcontent = rand(0,9);
//10>.=连续定义变量
$captcha_code .= $fontcontent;
//设置坐标
$x = ($i*100/4)+rand(5,10);
$y = rand(5,10);
imagestring($image,$fontsize,$x,$y,$fontcontent,$fontcolor);
}
//10>存到session
$_SESSION['authcode'] = $captcha_code;
//8>增加干扰元素，设置雪花点
for($i=0;$i<200;$i++){
//设置点的颜色，50-200颜色比数字浅，不干扰阅读
$pointcolor = imagecolorallocate($image,rand(50,200), rand(50,200), rand(50,200));
//imagesetpixel — 画一个单一像素
imagesetpixel($image, rand(1,99), rand(1,29), $pointcolor);
}
//9>增加干扰元素，设置横线
for($i=0;$i<4;$i++){
//设置线的颜色
$linecolor = imagecolorallocate($image,rand(80,220), rand(80,220),rand(80,220));
//设置线，两点一线
imageline($image,rand(1,99), rand(1,29),rand(1,99), rand(1,29),$linecolor);
}
//2>设置头部，image/png
header('Content-Type: image/png');
//3>imagepng() 建立png图形函数
imagepng($image);
//4>imagedestroy() 结束图形函数 销毁$image
imagedestroy($image);
?>After using the verification code file, you will get a picture similar to the following:
Click the verification code picture in the upper left corner, and the 4-digit number obtained will change.
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