With snowflake background PHP verification code generation program

Session_Start ();
$img _width=70; First define the length and width of the picture
$img _height=28;
$num _array=range (0,9);
$small _char_array=range (' A ', ' Z ');
$big _char_array=range (' A ', ' Z ');
$myarray =array_merge ($num _array, $small _char_array, $big _char_array);
$mystring = $myarray [Mt_rand (0,61)]. $myarray [Mt_rand (0,61)]. $myarray [Mt_rand (0,61)]. $myarray [Mt_rand (0,61)];
Exit ($mystring);
unset ($_session[' Shuzi '));
$_session[' shuzi ' = $mystring;
$aimg = Imagecreate ($img _width, $img _height); Generate pictures
Imagecolorallocate ($aimg, 255,255,255); Picture background, imagecolorallocate the 1th time to define color PHP is considered to be the background
$black = Imagecolorallocate ($aimg, 200,200,200); Define the required Black
Imagerectangle ($aimg, 0,0, $img _width-1, $img _height-1, $black);//A black rectangle to surround the picture

The following is the creation of a snowflake background, in fact, is to generate some symbols on the picture
For ($i =1 $i <=100; $i + +) {//test with 100 first
Imagestring ($aimg, 1,mt_rand (1, $img _width), Mt_rand (1, $img _height), "*", Imagecolorallocate ($aimg, Mt_rand (200,255) , Mt_rand (200,255), Mt_rand (200,255)));
In fact, is not a snowflake, is to generate the * number just. 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

Imagestring ($aimg, 5,mt_rand (5,35), Mt_rand (5, $img _HEIGHT/2), $mystring, Imagecolorallocate ($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);