copyright protection of images

One concern she has is copyright protection of slide images that might be put on the web site. They may want to have images available for teaching but they do not want people to link to the images or to take the images and use them without their permission. Are there effective mechanisms for copyright protection of images on a web site? I think they might consider adding digital watermarks, displaying a visible copyright message on images, and blocking search engines from crawling in certain directories. This
sort of deterence will probably work in many instances. I am wondering if there is image protection built into drupal (or any other cms) that is effective? Are there other measures that you think might work? For example, a closed web site (authenticated users), encryption (unable to open images stored in cache) or bringing up images in a separate application? I know nothing is perfect but she'll want an effective
strategy for protecting image content before moving ahead. What would you suggest?

You are correct in guessing that there aren't any really effective copy protections for images on the web or any digital platform, apart from watermarks. (People regularly ask to disable the right-click to save in JavaScript, but that only hinders the less technical users, and no matter what hoops you jump through, once you can see an image on your screen, you can simply take a screenshot.)

The best route: Drupal could provide smaller, watermarked images for all visitors and full-sized non- or less visibly watermarked images only to logged in, registered, trusted users.