Good question !
Looking in the mirror, I see a changing biological system with at least some resemblance to my last memory of the image. However, what the "I" is in this operation, other than a locus for comparison I am not sure. Some, have claimed that "self" is evoked by spasmodically within the praxis of living (Heidegger), or that it operates like a quarrelsome committee with a series of weak temporary chairmen (Ouspensky). And who was that "I" in that crazy dream last night, and where did it go when the body was not dreaming ?.
I think these questions are more fundamental than general epistemological or ontological ones.