Well, I think that we have interesting things here so far.
So I'd say ENFPs often express that crafty, vivid look, I'd say like they were smiling behind their faces.
I agree on what were said on INFPs - they can have dreamy expression, maybe innocent when they daydream about something idealistic, and I think there is also some kind of seriousness, but I'd call it idealistic seriousness, when INTP can have something like thoughtful seriousness.
...but another idea that came on my mind: we guys are talking here about static pictures, well, I mean, we have photos here, but they catch only static image. I think another interesting thing would be dynamic part of these gazes. I mean, how certain types BEHAVE with their eyes over time, not only how they look in one certain moment(into camera often).
One example, I know one INFP and she certainly express characteristic "dynamics" of eye movements. I noticed the very same "dynamic" in other types, but mostly in intuitives, in varying degree. I'd try to explain what exactly I observed: I would call it "visual gain", and it's about how many seen information do you actually process inside. You know, I look at that person's eyes and I see it's damn working down there in their head like hell; or another saying - they just damn understand what they see.
I'll finish it with simple saying - the people which do not express this thing ^^^ "look, but they don't see", but our person actually "look, but see, and understand what he/she see" I am very suspicious that this has something to do with intuiting function, maybe extroverted intuition. What do you think?