PHP Code:
<?php
function RandomStringGenerator($length){
global $string;
    $pattern = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890";
if(empty($length)){
    $length = "10";
    }
for($i=0; $i<$length; $i++){
    $string .= $pattern{rand(0,61)};
    }

return $string;
}

function CaptchaGenerator(){
global $string;
RandomStringGenerator();
header("Content-type: image/png");
$im = @imagecreate(100, 50)
   or die("Cannot Initialize new GD image stream");
$background_color = imagecolorallocate($im, 255, 255, 255);
$text_color = imagecolorallocate($im, 0, 0, 0);
imagestring($im, 10, 5, 5,  $string, $text_color);
imagepng($im);
imagedestroy($im);
}

CaptchaGenerator();
?>

PHP Code:
<?php

function RandomColorGenerator(){
global $red, $green, $blue, $color;
    $color = array(rand(50,255), rand(50,255), rand(50,255)); //generates random RGB color;
    $red = $color[1]; //red value;
    $green = $color[2]; //green value;
    $blue = $color[3]; //blue value;
}

function ShapeGenerator($vertices, $radius) {
global $points;
$points = array();
$degrees = 360/$vertices; //calculates the degrees per angle;


for ($i=0; $i<$vertices; $i++) {
    $cos = cos(deg2rad($degrees*$i)); //generates x points;
    $sin = sin(deg2rad($degrees*$i)); //generates y points;
    $cosTranslated = round($cos*$radius)+$radius; //translates x points;
    $sinTranslated = round($sin*$radius)+$radius; //transpates y points;
    $points[] = $cosTranslated; //Adds the x and y values to the array;
    $points[] .= $sinTranslated; //Adds the x and y values to the array;
    }
}

function RandomShape($sides,$radius) {
global $points, $red, $green, $blue;
RandomColorGenerator();
ShapeGenerator($sides, $radius);
    $vertices = count($points)/2;
    $image = imagecreatetruecolor(400, 400); //creates drawing canvass
    $bg = imagecolorallocate($image, 0, 0, 0); //sets the background color
    $color = imagecolorallocate($image, $red, $green, $blue); //sets the polygon color
    imagefilledpolygon($image, $points, $vertices, $color); //draws the polygon
    header("Content-type: image/png");
    imagepng($image);
}

RandomShape(rand(3,10), rand(25,200)); //DO IT!!!!!

?>