In parashat Tazria it mentions the Kohen's involvement of identifying tzaraat and rendering the person pure/impure (about 50 times!). Rashi (13:3) says that the Kohen's involvement in declaring 'pure\impure' is a gzeirat ha'katuv.
The Sefer HaChinuch says that:
“it is a mitzvah upon us, for anyone afflicted with tzaraat, to go to a Kohen (to enquire about about his tzaraat) who will make impure or purify him, and he [the Kohen] will act in accordance with the Torah…”
“the tumah and teharah is in the hands of the Kohen... If there is no knowledgeable Kohen [who can distinguish between different types] an sage of Israel shall see it and ask the Kohen to say ‘tamei’ and he will repeat ‘tamei’ [or vice versa with tahor]"
"Someone who became afflicted [with tzaraat]… but took this occurrence as happenstance and did not go to a Kohen, has nullified a positive commandment”
In the case of Miriam becoming afflicted with tzaraat (Bamidbar 12), she 'turns white' and is excommunicated from the camp for seven days until she becomes pure. It does not mention that she was 'declared' impure, and neither does the Torah mention that she becomes pure; rather that after seven days she was able to travel with her people.
It seems that the pure\impure status of a person/clothes/house is dependent on the declaration of the Kohen. What is the status of a person who has (what appears to be) the signs of tzaraat but does not seek a Kohen?