PHP Web site Verification code to generate snowflake background

The following is the referenced content:

<?session_start ();? >
<form method=post action= ">
<input type=text name=number maxlength=4>
<input type=" Submit "Name=" sub ">
</FORM>

/Check-check code
if (isset ($HTTP _post_vars["sub")):
if ($HTTP _post_vars["number"]!= $HTTP _session_vars[login_ Check_number] | | Empty ($HTTP _post_vars["number")) {
    echo "Check code is incorrect!";
}else{
    echo Verification code passed! ";
}
EndIf;
Show_source (' test.php ');
//above this page's source code

The following is the source code to generate the verification code
Show_source (' yanzhengma.php ');
?>
<?php
Session_Start ();
Session_register ("Login_check_number");
Last night saw the verification code effect on the Chianren, just consider it, using PHP's GD library to complete a similar function
First genetic the background, and then put the generated verification into the stacking
$img _height=120; First define the length and width of the picture
$img _width=40;
if ($HTTP _get_vars["act"]== "init") {
Srand (Microtime () * 100000); After//php420, Srand is not necessary.
For ($Tmpa =0 $Tmpa <4; $Tmpa + +) {
$nmsg. =dechex (rand (0,15));
}//by Sports98

$HTTP _session_vars[login_check_number] = $nmsg;

$HTTP _session_vars[login_check_number] = Strval (Mt_rand ("1111", "9999")); Generates a 4-bit random number and puts it in session
Who can make the supplement, can generate letters and numbers at the same time?? ----finished by Sports98.

    $aimg = imagecreate ($img _height, $img _width);   //Generate picture
    Imagecolorallocate ($aimg, 255,255,255);           //Picture background , Imagecolorallocate 1th time to define color PHP is considered to be the background of the
    $black = imagecolorallocate ($aimg, 0,0,0);        //define required black
    imagerectangle ($aimg, 0,0, $img _height-1, $img _ Width-1, $black);//First into a black rectangle to surround the picture

   //below this generates a snowflake background, which is actually generating some symbols on the picture
    for ($i =1; $i <=100; $i + +) {  & nbsp Start with 100 Tests
        imagestring ($aimg, 1,mt_rand (1, $img _height), Mt_rand (1, $img _width), "*", Imagecolorallocate ($aimg, Mt_rand (200,255), Mt_rand (200,255), Mt_rand (200,255));
       /ha, see it, in fact, is not a snowflake, is the generation of * No. In order for them to look "cluttered, 5-color, 6", they have to have their position, color, or even size randomly counted at 1 1, and rand () or mt_rand can do it.
   }

With the background generated, it's time to put the generated random numbers up. The reason is similar to above, random number 1 1 places, at the same time let their position, size, color are used into random number ~ ~
In order to distinguish it from the background, the color here is not more than 200, the above is not less than 200
For ($i =0 $i <strlen ($HTTP _session_vars[login_check_number]); $i + +) {
Imagestring ($aimg, Mt_rand (3,5), $i * $img _height/4+mt_rand (1,10), Mt_rand (1, $img _width/2), $HTTP _session_vars[login _check_number][$i],imagecolorallocate ($aimg, Mt_rand (0,100), Mt_rand (0,150), Mt_rand (0,200));
}
Header ("Content-type:image/png"); Tell the browser that the following data is a picture, not a text display
Imagepng ($AIMG); Generate PNG format ... The effect is quite like a matter of ...
Imagedestroy ($AIMG);
}

?>