define('PRAVIN_THUMBNAIL_DIR', '/home/firedev/public_html/wp-content/cache/thumbnails/');
function pravin_resize($img_path, $width, $height) {
    $resolution = '"' . $width . 'x' . $height . '"';
    $output_path = PRAVIN_THUMBNAIL_DIR . md5($img_path) . "-$resolution.jpg";
    // If file does not exist OR the thumbnail was generated more than 
    // 5 mins (5 x 60 sec) then re-create the thumbnail
    if(!file_exists($output_path) || (time() - filemtime($output_path)) > (5 * 60)) {
        system("/usr/bin/convert -resize $resolution $img_path $output_path");
    }
    return $output_path;
}