Under the General Settings you'll find a setting that will indicate to others that you do not want them to edit and repost your photos. It will not prevent them from saving your photos, but it will put a little 'Ok' or 'NOT Ok' to edit photos under your username in posts.
Right now everyone is set to yes, so if you do not wish for others to edit your photos, go ahead and change the setting
Right now everyone is set to yes, so if you do not wish for others to edit your photos, go ahead and change the setting