Yes you can 'Watermark' your pictures. But anyone determined enough will be able to clean it off. As for the other possibilities you allude to. I have to say it would be good if it they were possible, but very unlikely.
There are many things that you can do to try and protect photo's. However, once you launch them on the Web you are in effect giving them away.
The best solution I can offer you is save them in a format such as 'bmp' or 'jpg' and in a 'DPI' (dots per inch) that looks good in say a Postcard Size. That way if it does fall into the wrong hands, even if they can lift it from the Net. They won't be able to use it without a lot of knowhow and technical wizardry!