PHP implementation of verification Code steps and service-side check code

This article introduces to you about PHP implementation Verification code steps and service-side check code, there is a certain reference value, the need for a friend can refer to, I hope you have some help.

What is a CAPTCHA: A verification code is a public program that distinguishes whether a user is a computer or a person

Four steps required to make a verification code

1: Generate Basemap

2: Generate validation content

3: Generate Verification Code content

4: Verifying content

Step first, create a basemap:

Goal: Generate a 100*30-sized picture from PHP

Methods: Imagecreatetruecolor ($width, $height);

Caveats: Rely on GD extensions

Before outputting the image, the header information of the image must be printed in advance--"Send native HTTP header

The method defaults to output a black background

Imagecreatetruecolor () A new true color image is represented by a $image, which is then heavily used

Since it is to create a true color image, it will have a variety of colors, the following imagecolorallocate (choose the canvas, three-color parameters)

What do you want to fill imagefill (choose Canvas, start position, color)

To this, a basemap is generated, and the following begins with adding seasoning

$image = Imagecreatetruecolor (100,30)

$bgcolor = Imagecolorallocate ($image, 255,255,255);

Imagefill ($image, 0,0, $bgcolor)

Step two: Generate validation content

Goal: Randomly generate numbers (size, start position, content, color)

Method: Through the loop, imagestring function, horizontally generate a line of string (according to the imagestring inside the parameter position, to fill in)

Precautions: Control the font size, n/n

for ($i =0;$<4;i++) {

The variable is defined here according to the parameters inside the imagestring, and the variable is assigned a value

Imagestring ($image, $fontsze, $x, $y, $fontcontent, $fontcolor)

}

$fontcontent = substr ($data, Rand (0,strlen ($DATA)), 1);

If you want a combination of numbers and letters, the Substr method means that the substring of the string is returned, and the returned string gets the data randomly, starting with a maximum of 1 lengths

The third step is to generate the verification code content

Objective: To increase the interference element for the verification code, the interference element is a point or a line

Method: Imagesetpixel Point, imageline-Line (resource file, start position, color)

Precautions: Interference elements must control the color and quantity, avoid distracting

Fourth Step: Verify information through session storage

Target: Make record on server side, easy for user to enter verification code to do check

Method: Session_Start ()

Caveats: session_start () must be at the top of the script

Under multi-service situations, we should consider centralized management of session management

Imagepng exporting a picture to a browser or file in PNG format

Imagedestroy Destroying pictures good habit

In these methods, the use of resources is very much, that is, every method to $image this canvas

<php? $image = Imagecreatetruecolor (100,30), $bgcolor = Imagecolorallocate ($image, 255,255,255); Imagefill ($image, 0,0, $bgcolor);//for ($i =0; $i <4; $i + +) {//$fontsize = 6;//$fontcolor = imagecolorallocate ($image, Rand (0,120), Rand ( 0,120), Rand (0,120)),//$fontcontent = rand (0,9),//$x = ($i *100/4) +rand (5,10);//$y = rand (5,10);//Imagestring ($image, $    FontSize, $x, $y, $fontcontent, $fontcolor)//} $captch _code= "; for ($i =0; $i <4; $i + +) {$fontsize = 6;    $fontcolor = Imagecolorallocate ($image, Rand (0,120), Rand (0,120), Rand (0,120));    $data = ' abcdefhijkimnpqrstuvwxy345678 ';     $fontcontent = substr ($data, Rand (0,strlen ($DATA)), 1);    $captch _code.= $fontcontent;    $x = ($i *100/4) +rand (5,10);    $y = rand (5,10);    Imagestring ($image, $fontsize, $x, $y, $fontcontent, $fontcolor); } $SESSION [' Authcode ']= $captch _code;for ($i =0; $i <200; $i + +) {$pointcolor = Imagecolorallocate ($image, rand (50,200) , Rand (50,200), Rand (50,200)), Imagesetpixel ($image, Rand (1,99), Rand (1,99), $pointcolor);} for ($i =0; $i <3; $i + +) {$linecolor = Imagecolorallocate ($image, Rand (80,220), Rand (80,220), Rand (80,220)); Imageline ($image, rand (1,99 ), Rand (1,99), Rand (1,99), Rand (1,99), $pointcolor);} Header (' content-type:image/png '); Imagepng ($image);//end;imagedestroy ($IAMGE);? >

Verification code is made here, next is on the server side, do the calibration

Src= "captcha-2.php?r=<?php echo rand ();? > "   It's no big deal for this r to find information.

<image border= ' 1 ' src= ' captcha-2.php ' onclick= "this.src= ' captcha.php?t= ' + math.random ()" title= "Click to refresh"/> It's meant to be.

He still uses t here, so R ah T

For capitalization, use Strtolower () to convert all uppercase letters entered by the user into lowercase letters.

<?phpif (isset ($_request[' code ')) {    session_start ();    if (Strtolower ($_request[' code ')) {==$_session[' code '])    {        header (' content-type:text/html; Charset=utf8 ');        Echo ' 

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