Kim Eana (IU's lyricist), Park Yohan (IU's dancer) and Hanteo manager have commented on her photo (I'm way too lazy to scroll all the comments looking for more people I know.)

She is also following several people, like Coordi Noh, that require approval to be followed.

IU's confirmed Instagram account: link

[UPDATE] IU's former producer, Cho Young Cheol, confirmed the account on his twitter via his Instagram: link and IU replied.

Translation here: link

photo caption translation:
ee ji geum (wordplay of ‘Lee Jieun’, meaning ‘this now’) Instagram. Why does everyone add # at the back?

trans source: link

photo source: link