captcha.php

<?
session_start ();

switch ($_GET['a']) {
	case 'image':
      $_SESSION['captcha'] = substr(md5(uniqid("")),0,4);
    $im = @imagecreate (80, 20) or die ("Cannot initialize new GD image stream!");
		$bg = imagecolorallocate ($im, 101, 71, 37);
		$char = $_SESSION['captcha'];


		//âûâîäèì ñèìâîëû êîäà
		for ($i = 0; $i < strlen($char); $i++) {
			$color = imagecolorallocate ($im, rand(0,255), rand(0,128), rand(0,255)); //çàäà¸ì öâåò
			$x = 5 + $i * 20;
			$y = rand(1, 6);
			imagechar ($im, 5, $x, $y, $char[$i], $color);
		}

		//àíòèêåøèðîâàíèå
		header("Expires: Mon, 26 Jul 1997 05:00:00 GMT");
		header("Cache-Control: no-store, no-cache, must-revalidate");
		header("Cache-Control: post-check=0, pre-check=0", false);
		header("Pragma: no-cache");

		//ñîçäàíèå ðèñóíêà â çàâèñèìîñòè îò äîñòóïíîãî ôîðìàòà
		if (function_exists("imagepng")) {
		   header("Content-type: image/png");
		   imagepng($im);
		} elseif (function_exists("imagegif")) {
		   header("Content-type: image/gif");
		   imagegif($im);
		} elseif (function_exists("imagejpeg")) {
		   header("Content-type: image/jpeg");
		   imagejpeg($im);
		} else {
		   die("No image support in this PHP server!");
		}
		imagedestroy ($im);	
 break;

}
?>