It seems to be human nature to look at things and notice the construct of eyes, nose and mouth and the mind readily interprets it as a face. This basic need we have, perhaps something traced back to being a baby and needing to know what is feeding you, was a vital instinct but in investigation it can be a real difficult path that is often argued among researchers looking over evidence.
Let's have an interesting, if not sometimes hilarious, look at some examples.
Here is an interesting case where a construction crew was cutting out stone from a pit and went down to look at the work and found a face -
Some called it a demon face and even fled the site.
So, you can see how finding faces in orbs and other sorts of murky faces in window curtains and the like can be interpreted as spirit form. And, perhaps in some weird way, spirit is everywhere. But, proving a face shape means a spirit, well, it's usually dismissed for a reason.