Implementation of PHP Verification code ____php

Internship is to do a message, the message needs to verify the code.

PHP Verification code implementation, in fact, is the first random number, and then the drawing.

The key code is in validcode.php:

<?php 
	
	Header ("Content-type:image/png");
	
	Open session
	session_start ();
	
	Random 4 digits
	$code = "";
	$arr = Array ();
	For ($i =0 $i <4; $i + +) {
		
		$arr [$i] = rand (0,9);
		$code. = (String) $arr [$i];
	}
	
	Set into session, convenient than to
	$_session["validcode"] = $code;
	
	Start drawing
	$width = m;
	$height =;
	$img = Imagecreatetruecolor ($width, $height);
	
	Fill background color
	$backcolor = imagecolorallocate ($img, 0,0,0);
	Imagefill ($img, 0,0, $backcolor);
	
	Gets a randomly darker color for 
	($i =0 $i <4; $i + +) {
		
		$textcolor = imagecolorallocate ($img, Rand (50,180), Rand (50,180), Rand (50,180)); 
		Imagechar ($img, 12,7+ $i *25,3, (String) $arr [$i], $textcolor);
	
	Display Picture
	imagepng ($img);
	
	Destroy picture
	Imagedestroy ($img);
? >

Then use a page, place the IMG tag, and introduce the verification code. Then use a label for the user to switch the verification code to prevent the situation from being seen.