I recently had a client who told me he wanted all of his images “protected” from being downloaded. My answer was simple: “It’s not worth your time to persue that goal”. If someone who knows what he or she is doing wants an image, they’re going to get it by either examining your code, checking their cache or utilizing their print screen button.
Instead of wasting time with trying to block images, copyright them! Get yourself a watermark and place it on all of your pictures. There’s even a nifty little website that does it for you! Okay, this doesn’t work for every site, especially ones with a lot of images. For those I use something like this.