What is the process of designing verification code in php

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.

Related recommendations: "PHP Getting Started Tutorial"

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 will be used in the code Function:

mt_rand — Generate better random numbers

int mt_rand ([ int $min ], int $max ) Many old libc random number generators have some disadvantages Certain and unknown properties and very 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 a black image of size x_size and 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 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 is 0, 0 ) to 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() Use col color to draw in the image image A rectangle has the coordinates of its upper left corner as x1, y1 and the coordinates of its lower right corner as 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() Use color color in the image image from Draw a line segment 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() Draw the string s with col color Go 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() Output a GD image stream (image) in PNG format to standard output (usually a browser), or If a filename is given with filename then 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.

<img src="mycode.php"/>

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

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

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