iTunes syncs all iPad pictures every time

Hi, I am syncing photos in my iPad through my Macbook. The pictures are stored in an external drive. iTunes sees the library, that is correctly set. The thing is, I add 10 photos to the folder on the external drive, sync, and iTunes syncs ALL 3000 photos. Every time. Can't it see (after scanning the drive and the ipad) the 10 new ones and sync those ? It's so annoying and a waste of time. Is there a setting to overcome this, or another method altogether ?

Thanks,