It's because they both have rather high and chiseled cheekbones and they both have clefts in their chins. Shots where those features are highlighted lead most to see this resemblance including myself.
That's probably true but one's hair color definitely changes the way someone's features are noticed. As a blond, I look at Brittany's eyes and nose first. As a brunette, I look at her cheeks, hair, and chin.
ETA: Each picture is also different and there are many where she looks simply like herself.
ETA: Each picture is also different and there are many where she looks simply like herself.