PHP How to implement login verification code check function

This article is mainly for everyone to introduce the PHP implementation verification Code check function, with a certain reference value, interested in small partners can refer to

Verification code is implemented using the session function in PHP.
Declare the function session_start () at the top. Tell the server that we want to use this function.

Session_Start ();

The next thing we use is the code implemented by the verification code. Here is an example of the code for the English numerals.

$image = Imagecreatetruecolor (100, 30); Create a 100x30 Canvas $white = imagecolorallocate ($image, 255,255,255);//White Imagefill ($image, 0,0, $white);//Cover Black canvas

Then declare an empty variable before the verification Code implementation to hold the verification code.

$session = ""; An empty variable that holds the verification code for ($i =0; $i <4; $i + +) {   $size = 6;   $x = $i *25+mt_rand (5,10);   $y = Mt_rand (5,10);   $sizi _color = imagecolorallocate ($image, Mt_rand (80,220), Mt_rand (80,220), Mt_rand (80,220));   $char = Join ("", Array_merge (Range (' A ', ' Z '), Range (' A ', ' Z '), Range (0,9)));   $char = Str_shuffle ($char);   $char = substr ($char, 0,1);   Imagestring ($image, $size, $x, $y, $char, $sizi _color);   $session. = $char; Assign each value of the verification code to the variable}   $_session[' SESSION '] = $session;//The value of this variable is equal to the value entered by the user

for ($k =0; $k <200; $k + +) {   $rand _color = imagecolorallocate ($image, Mt_rand (50,200), Mt_rand (50,200), Mt_rand ( 50,200));   Imagesetpixel ($image, Mt_rand (1,99), Mt_rand (1,29), $rand _color); } for  ($n =0; $n <5; $n + +) {   $line _color = imagecolorallocate ($image, Mt_rand (80,220), Mt_rand (80,220), Mt_ Rand (80,220));   Imageline ($image, Mt_rand (1,99), Mt_rand (1,29), Mt_rand (1,99), Mt_rand (1,29), $line _color); }  header (' content-type:image/png ');//Set file output format imagepng ($image);//Export $image image Imagedestroy ($image) in PNG format; Destroying images

Use POST to receive the verification code. The Strtolower function is to make the server case insensitive. This can effectively reduce the user's error rate.

if (Isset ($_post[' Session '))) {   session_start ();   if (Strtolower ($_post[' Session ')) ==strtolower ($_session[' Session ')) {     echo ' <font color= ' #0000CC ' > input correct </form> ';   } else{     Echo ' <font color= "#CC0000" ><b> input error </b></font> ';   }   Exit (); }

The following is the HTML page code.

<! DOCTYPE html>