//create high quality aspect true thumbnails for all the files in a given directory
if ($handle = opendir('path/to/directory/')) {
    echo "Directory handle: $handle\n";
    echo "Processing Entries:\n";    
    while (false !== ($entry = readdir($handle))) {
        $isThumb = strpos($entry, 'thumb');
        if ($entry != "." && $entry != ".." && $isThumb === FALSE) {
            //echo "$entry\n";//debugging
            $filename = $entry; //for readability, now that we know its a valid filename.            
            $width = 175;   // maximum width
            $height = 175;  //  maximum height
            header('Content-Type: image/jpeg'); // set content type
            // Get new dimensions
            list($width_orig, $height_orig) = getimagesize($filename);
            $ratio_orig = $width_orig/$height_orig;
            if ($width/$height > $ratio_orig) {
                $width = $height*$ratio_orig;
            } 
            else {
                $height = $width/$ratio_orig;
            }
            // Resample image
            $image_p = imagecreatetruecolor($width, $height);
            $image = imagecreatefromjpeg($filename);
            imagecopyresampled($image_p, $image, 0, 0, 0, 0, $width, $height, $width_orig, $height_orig);
            // Output
            $newFileName = "thumb-" . $filename;
            //echo "thumb $newFileName created"; //debug
            imagejpeg($image_p, $newFileName, 100);
            imagedestroy($image_p);
        }
    }
    closedir($handle);
}