You have no idea how pretty and attractive and a million other things that your photo makes me feel. It may be a photo that everyone can enjoy, but it means an order of magnitude more than that to me. To me, that photo represents what most women spend thousands of dollars on wedding photos for - proof for the ages of vitality, of attractiveness, of youth (ok, so not-so-much youth for me, hehe) -- the details vary but the theme remains. Your example of a photo that has no need for a mnemonic is exactly the opposite to me, because in 20 years, this photo will bring to life the memory of what it is that I am now, for the small group of people who knew me. And not just a shady memory, but an idealized, perfected memory at that...When Pam says You have no idea how pretty and attractive and a million other things that your photo makes me feel, my photographer's ear hears "You have included the things I like best about myself in the picture, and you've left out the things I don't like about myself".
This doesn't always happen. Sometimes I take a picture I think is beautiful, but which the subject hates. When this happens, everyone else I show the picture to agrees with me that the picture is beautiful. In cases like this, the subject always has some very specific complaint ("my nose looks big", or "my eyes are different sizes").
In both cases - when the subject likes the picture and when she doesn't - I feel like I've succeeded because I've taken the photo I wanted to take: a photo which communicates what I find beautiful about the subject to almost everyone. But the first case - Pam's case - is better, because Pam agrees with everyone else that there's something beautiful about her which I've captured in the picture.
The best case of all, of course, is when this is news to the subject - the photographer's dream is to hear his subject say "No one has ever taken a picture that good of me - I didn't know I was that pretty".
This can happen because we all have mental pictures of ourselves which don't correspond exactly to reality. When Pam calls her picture an idealized, perfected memory, on one level she's just being literal; I did pose her and light her to best advantage, and I did do a little retouching to clean up stray hairs and things, so the picture is "idealized" and "perfected" to some extent.
On another level, though, what Pam is saying is that the picture on your screen looks better than the picture of herself she carries around in her mind.
This isn't neurotic; most people's mental images of themselves are less attractive than the real thing. I can't count the number of times people have told me "I'm not photogenic", when what they really mean is "I don't like my nose, and it makes me unhappy when I see it in pictures". I also can't count the number of times people who have said this to me have loved a picture I've taken of them. These people are surprised at how good their pictures look because when they're looking in the mirror (or at casual snapshots taken without any attention paid to posing and lighting), they're focusing on things they consider unattractive, but when I'm looking in the camera's viewfinder, I'm focusing on things I consider attractive - and figuring out how to leave everything else out of the picture.
At this point, you might accuse me of lying with the camera, or of contributing to unreasonable standards of feminine beauty, flacking for the cosmetics industry, etc...
But wait a minute - my image is no more a lie than Pam's mental image; neither is "the truth" - they are both just stories. If you could print out Pam's mental picture and lay it beside the picture on your screen, different people would have different opinions about which story is more "true". Pam would say her mental picture is closer to the truth; I would insist that my picture is closer to the truth. You, dear readers, would argue amongst yourselves.
Our self-images consist, of course, of more than just pictures. Our self-images are stories (An Identity is a Story), and we construct stories about all aspects of our lives and personalities. Our versions of those stories differ in lots of ways from the stories other people make up and tell about us (Identity is Subjective). This is why flattery works; we like it when we hear a story about ourselves which is prettier than our own version. It's also why gossip hurts - nobody likes it when a third-person account of "his story" compares unfavorably to the "official" first-person version.
And, of course, it's why we can be surprised - delighted or depressed - by pictures of ourselves. Surprises like this can change us; I like to think that Pam's mental picture of herself is a bit prettier than it was before she saw my picture of her.