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Front surface mirrors are also used in cameras, specifically SLR and TLR cameras. Like in the above, it's in order to prevent double images.

This is why you never want to touch the mirror in your SLR camera when you have the lens removed. Because it's a front surface mirror, it's very, very easy to scratch the reflective coating off.

But then again, it's just annoying, since the effect would only show up in the viewfinder, and not on the photograph itself.