I think that being able to blend in so they can observe people undisturbed is more important than any particular style. That and the Se is 4th function and doesn’t usually kick in until later (twenties? thirties?), so there’s a potential lack of or disinterest in self-awareness as relates to image for INFJs.
As adults with some more interest in their Se, there’s maybe an image control thing, where they will make the effort before to look nice for things like photos, which might be seen by family or co-workers or posted to the internet. In my case, I don’t really think about it that much unless I see the photo after and look terrible – I have a lot of family photos where I’m just pulling stupid faces. (Good examples of stupid INFP faces can be found here.)
I also have the bias of being the only P type in a J type family, so everyone seemed less resentful of hair brushing than me. (What is the point?? It will only knot again two minutes later??)