Something

   $node->field_photoset = array  
    (
        0 => array
            (
                'fid' => 'upload',
                'filename' => $img_large_name,
                'filepath' => $img_large_path,
                'filemime' => 'image/jpeg',  // the appropriate mimetype
                'filesize' => filesize($img_large_path)
            )
    );
    
    node_save($node);