I don't know anything about Instagram. I had the app on my phone for a while but it seems to have gone, maybe I deleted it.
I have a few friends who post quite often on Instagram but I only know this because I see them on Facebook.
When I did have Instagram I noticed that some of my actual friends were following me, even though I never posted a single thing, but maybe I followed them first.
Anyway, very long-winded explanation to show you the level of ignorance you are dealing with here, if you look at someone's Instagram account/pictures/home page or whatever it is, do they know that you have looked at it? How do they know? Can they see you looking?
I read somewhere that this happens. Person A looks at person B's Instagram and person B knows that person A has looked including their identity. Do you need to have an Instagram account yourself to look at people's accounts? You don't with Twitter, I don't think.
Thanks if you can enlighten me.