Oh yeah… Prosopagnosia is the cognitive impairment of facial recognition. It’s super plausible with Luffy. People with prosopagnosia usually need to reply on other indicators to identify people, like hair style/color, body shape, voices, clothing, and so on.
He’s got green hair, three swords, and a white shit, so he’s gotta be Zoro, right? And he’s got blond hair, curly eyebrows, and smokes, so he’s gotta be Sanji. And it also makes sense for how Luffy thinks that Sanji and Duval and Sanji’s wanted poster look the same.
If Luffy (and Oz, who had Luffy’s personality and mind) can only differentiate faces based on their object features (hair color, hair style, eyebrow shape, etc.), rather than the face itself as a whole, it would make sense that to Luffy, there’s no real difference between how Sanji and his poster look.
And it would also make sense with how Luffy often gives people nicknames based on their physical appearance, like calling Kuma “that bear Shichibukai” (because of his size and his hat, which has bear ears on it), calling Shiki “steering wheel,” and even calling Bartolomeo “chicken head.” If Luffy is able to focus on a specific, very distinct object feature of a person’s appearance, I imagine it makes recognizing them a lot easier.
I only wrote about Luffy here, but it’s super likely that Zoro has some kind of topographical disorientation. I think he could have heading disorientation or topographical agnosia, though I think the first might be more likely. Zoro seems to be unable to comprehend what north is, and equates it with up, and has a hard time telling left and right apart, or conceptualize things like “go right at this landmark.” He could have both tho.