$imgFolder = "/imagens/bg"; // the path from the sites root to the image folder created at 3 above
$element = "header"; // the css ID of the element to apply the background image to
// That's it!! Nothing below this line needs to be changed
$img = null;
// build up the path to the image folder
if (substr($imgFolder,0,1) != '/') {
$imgFolder = '/'.$imgFolder;
}
if (substr($imgFolder,-1) != '/') {
$imgFolder = $imgFolder.'/';
}
$path = $_SERVER['DOCUMENT_ROOT'] . $imgFolder;
// populate an array to hold valid file type extensions
$extList = array('gif','jpg','jpeg','png');
// create an array to hold the list of image files
$fileList = array();
// open a handle to the directory
$handle = opendir($path);
// loop through the contents of the directory
while ( false !== ( $file = readdir($handle) ) ) {
// get the info for each file
$file_info = pathinfo($file);
// check that the file in in the allowed extensions array
if ( in_array( strtolower( $file_info['extension'] ), $extList)    ) {
// add the file to the array
$fileList[] = $file;
}
}
// close the handle to the directory
closedir($handle);
// if we have at least 1 file in the list
if (count($fileList) > 0) {
// select a random index from the file list array
$imageNumber = time() % count($fileList);
// assign the filename for that array index to the $img var
$img = $imgFolder . $fileList[$imageNumber];
$css = "#$element { background-image: url('".$img."'); }\n";
// tell the browser what we're sending
header('Content-type: text/css');
// and write out the css
echo $css;
}
?>