Billedskift ved klik

En enkelt PHP side placeret i samme folder som billederne ligger i - nemt og smertefrit! PHP filen kaldes som et billed (img)
Kode (XHTML, PHP, CSS etc.): 
***PHP FILEN "KALDES"*** <img src="http://www.din-hjemmeside.dk/mappe-hvor-filen-og-billeder-er/rotate.php" alt="" /> ***PHP FILEN ***<?php $folder = '.'; $extList = array(); $extList['gif'] = 'image/gif'; $extList['jpg'] = 'image/jpeg'; $extList['jpeg'] = 'image/jpeg'; $extList['png'] = 'image/png'; $img = null; if (substr($folder,-1) != '/') { $folder = $folder.'/'; } if (isset($_GET['img'])) { $imageInfo = pathinfo($_GET['img']); if ( isset( $extList[ strtolower( $imageInfo['extension'] ) ] ) && file_exists( $folder.$imageInfo['basename'] ) ) { $img = $folder.$imageInfo['basename']; } } else { $fileList = array(); $handle = opendir($folder); while ( false !== ( $file = readdir($handle) ) ) { $file_info = pathinfo($file); if ( isset( $extList[ strtolower( $file_info['extension'] ) ] ) ) { $fileList[] = $file; } } closedir($handle); if (count($fileList) > 0) { $imageNumber = time() % count($fileList); $img = $folder.$fileList[$imageNumber]; } } if ($img!=null) { $imageInfo = pathinfo($img); $contentType = 'Content-type: '.$extList[ $imageInfo['extension'] ]; header ($contentType); /* fixes cahce issue, thanks to dchapiesky */ header( "Expires: Mon, 20 Dec 1998 01:00:00 GMT" ); header( "Last-Modified: " . gmdate("D, d M Y H:i:s") . " GMT" ); header( "Cache-Control: no-cache, must-revalidate" ); header( "Pragma: no-cache" ); readfile($img); } else { if ( function_exists('imagecreate') ) { header ("Content-type: image/png"); $im = @imagecreate (100, 100) or die ("Cannot initialize new GD image stream"); $background_color = imagecolorallocate ($im, 255, 255, 255); $text_color = imagecolorallocate ($im, 0,0,0); imagestring ($im, 2, 5, 5, "IMAGE ERROR", $text_color); imagepng ($im); imagedestroy($im); } } ?>