I think in the Harry case, the people who had known his parents were specifically looking for family resemblances. When you really look at the child of someone you know, you can usually pick out a couple of features that remind you of the parents, even if it's more a creative re-envisioning.

But the "tri-colored rings of smoke and ice and smoke-covered ice with little sparkly lightning bolts in them and big long eyelashes and just a touch of pretty, pretty eyeshadow" thing that LKH does makes me wanna hurl.