Willis, 22, said the pictures were designed to protest the policies of Instagram, which takes down the accounts of members who violate its policy by posting pictures of female breasts in which the nipple is exposed.
"This is about helping women feel empowered, to make personal choices about their bodies not dictated by what society says is decent," Willis wrote Thursday on Twitter under the hashtag #freethenipple.
The photos showed Willis shopping topless at a fruit and vegetable stand and walking down the street. "Legal in NYC but not on @instagram" she tweeted.
Instagram, which is owned by Facebook, said its policies were designed to keep the service a "fun and safe place" with guidelines that" put limitations on nudity and mature content."
DPA