For most people, faces are stored in the brain as a single piece of information, and when they see a familiar face they instantly know who it is. Memories of human faces are actually stored in a specialized place in the brain, and there is evidence to suggest that lesions in that part of the brain may cause prosopagnosia (face-blindness), or at least contribute to it. Whatever the reason, I don't have the ability to recognize faces as a whole.
I can remember an individual feature but each one is stored separately. So I have to scan a face for eye shape (upper lid, lower lid, length, width), nose shape/size, lips shape, eyebrows, jawline, cheek shape, coloring -- each piece running though every stored feature and filtering out people who don't match the features met so far. To put it another way, where your average person sees "8" I see "1+1+1+1+1+1+1+1" only it's much harder because each piece has so many possible shapes. The idea of recognizing an adult by their child photo is so unfathomable to me, because all the features have changed size at least and everything looks different.
I always have to put effort into recognizing people. It usually takes at least three filtering steps before I realize who it is, and that takes more time when it is out of context or when it has been a long time since I have seen someone because I store features by how soon and in what context I expect to see them. I have gotten good enough at my work-arounds that it is not often that I talk with someone for more than 15 seconds without realizing who that is, but that's partly because I am using their voice and movements to help me place them.
The most familiar face in my life was the person I knew for 12 years before we got married and then we lived together and saw each other almost every day for 6 years. Even at the end of that, if I saw them in a place I wasn't expecting to see them, it would take me a few seconds to realize who it was. Imagine seeing the face of your long-time live-in lover and having to study it for 3 whole seconds before you knew who it was.
I use non-face shortcuts with people I don't know whenever possible, but that can lead to a mess. There are three women at my office with similar coloring and hairstyle -- pale with shoulder-length straight blonde/light brown hair parted at 3/4ths and cut bluntly across at the bottom -- and it took me weeks to realize they were different people and months to be able to remember which one was which. Even though they look nothing alike, don't dress alike or act alike, and don't work in the same department! but their skin is very flat in coloration (they probly wear foundation) and not very different from their hair so without staring it is hard to make out the edges of their features. Also that hairstyle is unusual (there are no layers or face-framing) so I was using it as a shortcut as I didn't expect more than one!
This is part of the reason I find unusual faces so attractive; they are easier to place so it gives me a sense of relief, which I feel every time I see them. I also love faces with sharp delineations of their features and people who habitually wear eyeliner and/or have dark eyebrows because I don't have to mentally trace the outline before I scan my memory for that feature. Conversely, I get irrationally irritated when more than one person has the same "unnatural" hair color, especially if they have similar skin coloring. Why are you fuckin up my cheat sheet?! I want no more than one blue-haired person in my life at a time okay? ideally everyone I cared about would look completely different from everyone else I cared about even at a distance of 500 feet.
This inability to see faces as a whole can be hacked in one way: photos and sometimes videos. Because they get stored in my brain as a whole image, I can remember them better than a live face. I am better at recognizing celebrities than most people because I've never seen them live, only on a screen or page. It has happened quite often that I see an actor playing a minor character for the second time in a very different role, and I will figure out where I remember seeing them while the non-prosopagnosiac next to me is completely surprised that it is the same person even though they had the same exposure that I did.
This memory hack makes it really important to me to see photos of people I love. As I told a friend recently, it makes people feel more real to me. I had a crushing moment about 2 years ago when I realized that part of the reason it was so difficult for me to feel secure in being loved was that I can't pull up an image of someone smiling at me lovingly, so even though I knew it had happened, it felt like it never did. When I talked about it with Topaz 2 years ago, they finally got why I always wanted to take photos of them, and they started sending me photos of themself. I definitely think that a big part of why I feel so loved by them is that they do this.
Still, they don't like being looked at and they are uncomfortable with me taking their photo. The other day I was cuddling with Topaz and started trying to take a photo of them, but couldn't get one that worked, so kept deleting and trying again. They got self-conscious and hid their face and asked why I was taking "so many" photos. I told them that I didn't have any photos of them making that face so I was trying to capture it, and they asked "what face?" I said "that 'I love you' face." They then tried to let me take the photo but the feeling had been interrupted and the face was different. I feel really sad now that I couldn't capture it because even the blurry impressionist memory of it is gone.
Part of the reason I always felt so loved and connected and real with Hannah and Kylei was because we took photos of each other all the time and they were comfortable enough with a camera that when I went to take a photo, that act didn't change the feeling of the moment. I could actually take photos of them in a particular emotion without it vanishing in front of the camera. Then we would look at our photos together, so I had visual memories of connecting with them. My memory is deeply terrible; to have memories of my life, I have to study. Without photos or journal entries, I have nothing to study, so the memory is just lost. Most of my experiences are lost to me within a week.
It feels so unfair that other people don't have to ask permission before storing a face in their memory, but I do because I can only do it with a camera. It feels so unfair that others don't have to disrupt the experience in order to create a memory of it.
I think people who can pull up visual memories of people acting loving towards them have no idea what a gift it is to have that mental evidence of love. It took me years to even be able to get the impression of Topaz' face that I use to feel loved: a corner of one eye crinkles in this particular way when they are feeling charmed by me. I can pull up a blurry impressionist image of this and the feeling of the rest of their face is there even though I can't imagine it. I cling to that tiny fragment of face memory with all my might.