Detailed explanation of examples of making verification codes based on PHP

This article mainly introduces PHP to create verification codes. Using PHP to verify website verification codes is set up to prevent malicious registration, brute force cracking or batch posting of programs.

Website registration, login or message page all require a registration code to verify the legitimacy of the current operator, in order to prevent the website from being maliciously registered by machines.

Generating a verification code is nothing more than a few steps. First, get a random string, then create a canvas, write the generated string on the canvas, and we can also draw lines on the canvas. Draw snowflakes and now post a code that generates a verification code.

Source code:

<?php
session_start(); //开启session
//创建随机码，并保存在session中
for($i=0;$i<4;$i++)
{
$_nmsg.=dechex(mt_rand(0,15));
}
//保存到session中
$_SESSION[&#39;code&#39;]=$_nmsg;
//设置图片长和高

$_width=75;
$_height=25;
//创建一张图像
$_img=imagecreatetruecolor($_width,$_height);

//白色背景
$_white=imagecolorallocate($_img,255,255,255);
//填充到背景上
imagefill($_img,0,0,$_white);

//黑色边框
$_black=imagecolorallocate($_img,0,0,0);
imagerectangle($_img,0,0,$_width-1,$_height-1,$_black);

//随即画出5个线条
for($i=0;$i<5;$i++)
{
$_rnd_color=imagecolorallocate($_img,mt_rand(0,255),mt_rand(0,255),mt_rand(0,255));
imageline($_img,mt_rand(0,$_width),mt_rand(0,$_height),mt_rand(0,$_width),mt_rand(0,$_height),$_rnd_color);
}

//雪花
for($i=0;$i<10;$i++)
{
$_rnd_color=imagecolorallocate($_img,mt_rand(200,255),mt_rand(200,255),mt_rand(200,255));
imagestring($_img,1,mt_rand(1,$_width),mt_rand(1,$_height),"*",$_rnd_color);
}

//输出验证码

for($i=0;$i<strlen($_SESSION[&#39;code&#39;]);$i++)
{
imagestring($_img,5,10+$i*15,mt_rand(0,10),$_SESSION[&#39;code&#39;][$i],$_blackr);
}

//输出图像
header(&#39;Content-Type:image/png&#39;);
imagepng($_img);
//销毁图像
imagedestroy($_img);
?>

##The following functions will be used in the code:

mt_rand — Generate better random numbers

int mt_rand ([ int $min ], int $max ) Many old libc random number generators have some uncertain and unknown characteristics and are slow. PHP's rand() function uses the libc random number generator by default.

The mt_rand() function is informally used to replace it. This function uses the known features of Mersenne Twister as a random number generator, which can generate random values ​​​​on average four times faster than rand() provided by libc.

dechex — Decimal to hexadecimal conversion returns a string containing the hexadecimal representation of the given number argument. The maximum value that can be converted is 4294967295 in decimal, which results in "ffffffff".

imagecreatetruecolor — Create a new true color image

resource imagecreatetruecolor (int $x_size, int $y_size)

imagecreatetruecolor() returns an image identifier, representing an image of size x_size and Black image of y_size.

imagecolorallocate — Assign a color to an image

int imagecolorallocate ( resource $image , int $red , int $green , int $blue )
imagecolorallocate() Returns an identifier representing the A color composed of the given RGB components. red, green and blue are the red, green and blue components of the desired color respectively. These parameters are integers from 0 to 255 or hexadecimal 0x00 to 0xFF. imagecolorallocate() must be called to create each color used in the image represented by image.

imagefill — area filling

bool imagefill (resource $image, int $x, int $y, int $color)
imagefill() at the coordinates x, y of the image image (the upper left corner of the image (0, 0), perform area filling with the color color (that is, points with the same color as the x, y point and adjacent points will be filled).

imagerectangle — draw a rectangle

bool imagerectangle ( resource $image , int $x1 , int $y1 , int $x2 , int $y2 , int $col )
imagerectangle() uses col color Draw a rectangle in the image, with the coordinates of its upper left corner being x1, y1, and the coordinates of its lower right corner being x2, y2. The upper left corner of the image has coordinates 0, 0.

imageline — draw a line segment

bool imageline ( resource $image , int $x1 , int $y1 , int $x2 , int $y2 , int $color )
imageline() uses color color Draw a line segment in the image image from coordinates x1, y1 to x2, y2 (the upper left corner of the image is 0, 0).

imagestring — draw a line of string horizontally

bool imagestring ( resource $image , int $font , int $x , int $y , string $s , int $col )
imagestring() Use col color to draw the string s to the x, y coordinates of the image represented by image (this is the coordinate of the upper left corner of the string, and the upper left corner of the entire image is 0, 0). If font is 1, 2, 3, 4 or 5, the built-in font is used.

imagepng — Output an image in PNG format to a browser or file

imagepng() Outputs a GD image stream (image) in PNG format to standard output (usually the browser), or if using filename If a filename is given, output to that file.

imagedestroy — Destroy an image

imagedestroy() Releases the memory associated with image.

Save the source code as code.php is a php file, how do we use it?

imagepng has output this php file into a png file

Just call it directly

8f14cf8be6b010acf0b53b17391f56e4

If you want to use the verification code, remember to open the session

<?php
session_start();
echo $_SESSION[&#39;code&#39;];
?>

Summary: That’s it for this article The entire content of the article is hoped to be helpful to everyone's study.

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