Is this obvious enough?

I have learned over the past few months that being a photographer and running a business are two very, very different things. I've enjoyed (mostly) every second of my shoots, I love meeting families and having fun at our shoots.
HOWEVER... I learn something new every day and today I learned that I am too trusting!
Today, I found out that some people had right clicked and saved the images from their online gallery and then reprinted the web sized images. Web sized images are... web sized. They're not meant to print. They are about the size of a wallet at their largest. So, if you blow it up to normal, it looks blurry, pixelated and, well, crappy.
I know I should have been watermarking all along, but honestly it felt silly. I really trusted that people would know better. And most everyone has- nearly every single client has placed their order quickly and simply, even when they know they could get cds for cheaper, they have opted to order through me and I appreciate it. It tells me that they value the work I did, and that's nice.

BUT, for those that don't seem to understand that I work for hours traveling to a shoot, taking the pictures, editing the pictures, and then preparing the orders, do you think they'll understand THIS?

Am I correct in assuming that a big fat copyright over kids faces will stop people from stealing my stuff? ;)