You should have browsing off for that directory. So, if you do that, someone would have to work pretty hard to copy the images. The "Save As" option is always there unless you provide some JS to circumvent the right click menu, but if you do that, you might make some visitors mad. It all depends on who you are selling to.
Presumably, your images are not as expensive as the product . . . but I don't know the specifics. BUT, I can say that this particular issue has never come up. More importantly, it's not a function of or implementation "bug" in dC.
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~ ChrisOpen Source = Community = Shared Responsibility = Submit A Patch!