I have to wonder about this feature. There is no way to prevent someone from downloading a publicly viewable file. In fact, they HAVE to download it in order to view it. Here are a couple of ways to "break" this so called protection:
1) Disable javascript in your browser, or tell it to ignore silly requests like "disable right click."
2) Retrieve the image from your browser cache. Hell, there is a FireFox addon that lets you search for, and view, images in your cache.
3) Use curl, grep, and some regex magic to download the image.
I mention this because sites that try to cripple my mouse upset me. I use the context menu to navigate backward in my browsing history without having to move to the toolbar.