Ask yourself this:
If showing your pictures is important then the risk people might take them has to be considered against how valuable they are to you.
The tightest security know to man is enough to stop people stealing your photos.... It's called cutting the power cord. Short of that, not a single method will give you all the protection.
I've been through this and now use SME to require clients to login before seeing their photos. Cut down unauthorised downloads by 60%. Cut down my sales by 90%
Roll your dice and take your chances. Watermarking is only partly successful too. Shareware authors take this risk every day. Just look at the metoric rise of sausage software. Sometimes giving a little get the most in return.