With MarcSpider's evidence of downloading, you have a very strong case for pursuing a copyright infringement case against the infringer who willfully downloads such a protected image. That's the short of it. But since Digimarc comes with the most popular graphics applications, it makes sense to use it out of the box. Here is a selection of Web sites of other watermarking products for you to do a quick review. No longer the stuff of super-secret spy rings, encryption has moved well into the domain of the everyday computer graphics user.
Encryption is a way of protecting the content of messages.
With Pretty Good Privacy encryption software, for instance, the form of encryption is called public key. It can be used on any digital file, text, or graphic. So this works when you want to send or post something securely, but only the people who have your key can see it. You can choose to protect your Flash file so that others can't take and reuse parts of it. So while it does offer a level better than HTML, I wouldn't call it secure.