$old = get_post_meta($post_id, '_ppwfg_images', true);
$newppwfgimages = array();
$thumb = $_POST['ppwfgthumb'];
$full = $_POST['ppwfgfull'];
$count = count( $full );

for ( $i = 0; $i < $count; $i++ ) {
    if ( $full[$i] != '' ) {
        $newppwfgimages[$i]['ppwfgthumb'] = stripslashes( strip_tags( $thumb[$i]) );
    }
}