Okay, sorry for the long post, I tend to be verbose.

So I noticed at the park yesterday, a woman with dark hair was looking at me like she knew me, she was chatting to a friend, and I would smile(just in case I did know her), and carried on w/my kids. Everytime I was near her, she would pause and shift her body weight in such a way that people do in anticipation of a person approaching. When I passed by her, not approaching, her body language relaxed, and she resumed her conversation. I saw a kid that I thought I *might* have known, he had brown hair, which is distinctive for here. But I found nothing to tie the two together so I wasn't sure if it was the lady I exchanged info with and invited to hang out with. I tried to remember her and her son, but all I remember is a tall shape and a small brown haired boy, their family story but no faces. Upon reflection, I think that was the lady I made friends with the other week.

I can recognize animals, the only way I used to recognize friends before was with what dog they were walking, and I used to bring my dog with me on outings, if he recognized someone, I knew we were friends based on their interaction.
Now I have to recognize friends based on their kids or their own faces, no animals to help me. I can recognize red-haired people, or curly haired people(but only if it's dark hair). And if the person wears sunglasses, forget about it, might as well put a bag over their head. I will forget them the moment I walk away. I try to memorize their facial features when they are talking but I just don't remember, and it seems like there is an unspoken expectation that if one hangs out for a particular amount of time, one is expected to recognize them or their kin.

So any tips on how to recognize or retain memory of people's faces?