expression
as anyone can see; obviously; clearly
Used to emphasize that something is obvious or undeniable to any observer. Often appears at the beginning of a sentence or clause.
誰が見ても、彼は疲れている。
Anyone can see that he is tired.
誰が見ても、この絵は素晴らしい。
This painting is clearly wonderful, as anyone can see.
どう見ても means 'no matter how you look at it' and is more subjective, while 誰が見ても is more objective, implying any person would agree.
A fixed phrase composed of 誰 (who) + が (subject marker) + 見て (te-form of 見る, to see) + も (even). Literally 'even if who sees', it has become a set expression meaning 'as anyone can see'.