I'm not against security, actually I am a strong advocate of web security in general. It is just that digital information is, by it's nature, portable. It is designed to be copied. You can't change that.
Simply put. If you are worried about an image being stolen, don't post it on the internet. Pretty much any security measure you can come up will be bipassed by a determined thief, or even a casual one. A determined thief will definitely crack any security measure you can put up.

The problem, if that is the right word, is that for a document to be displayed, it is already loaded into the client computer. A Pragma no-cache metatag will stop the page from being cached, but it won't stop the page from being loaded in the first place (and it is hell on your bandwidth). IE can't access html, but most other browsers can, so blocking the source code doesn't help either.

Ultimately, you can't stop digital theft. Which raises the question: Why try?
Disabling right-clicks, water (and other) marks, and most every other security measure do nothing more than deter the average (which I believe is an honest) viewer from properly viewing your pictures. None of them are going to stop a thief. A signature will be painted out, watermarks removed, etc., if somebody want's to steal your work. 

I was really bummed out when I came across one of my pictures with my signature pixelled out and someone else's name there. Why anybody would want to steal my pictures, I don't know. At any rate, I don't even put a signature on anymore, I just do the following:

Never ever post a full size picture. Post the 1024x768, but keep the 2048x1536 for yourself. Or crop the original and post the cropped version on the net. Then if it should ever become neccessary that you prove an image is your property, you can easily produce a larger, higher quality image than the other party in question.

For a professional gallery, I would think that .htaccess password would be the way to go. Passwords will be cracked too, but that is more difficult and automatically a criminal action.

Friends don't let friends use booleans.