Here is the gist of the post:
An ingenious study published in Personality and Social Psychology Bulletin (PDF) looked at how well people knew their own face. They took neutral photos of people and morphed their images to different degrees to either be more "attractive" (like a composite face) or "less attractive" (people with craniofacial syndrome). They then asked the participants to choose their actual, unmorphed photo from the variety of choices.
But instead, more than half the participants picked the morphs that were more attractive (even by their own opinions) than their real photos. In other words, they thought they were hotter than they really were....
Participants in the study were also asked to do the same lineup-picking for close friends, and their bias towards attractiveness also extended to them.
I actually remember making this hypothesis long ago, and wanting to test it in a similar way. My "data" were that when I saw people I knew well in a mirror, like family, I was surprised at how asymmetrical they looked to me. Of course symmetry is linked with attractiveness, thus the link with the work above. Back then, I hypothesized that I was somehow correcting in my mind for people's asymmetries. Similarly, when I saw a double-reflection of myself, I was struck by how asymmetrical (=ugly) I actually am, compared to what I "see" when I view my single reflection. Again, I was somehow correcting for my own asymmetries when viewing my reflection, and that correction didn't work the same when seeing a double-reflected image.
I haven't had a chance to read the original paper, but here is an extension based on my nerdy observations of the world: I think this symmetry-enhancement extends to pets. I remember seeing my cat PeeWee in the mirror, and being struck in the same way at how asymmetrical her reflection appeared to me.
I remember trying to explain this to some friends once. They thought I was crazy. So I thought maybe I am the only one who experiences this reflection asymmetry shock. The work described at OoaN makes me feel like I might not be the only one!