"The picture is inappropriate and should not have been taken," Marin said during a press conference on Tuesday in Helsinki with President Sauli Niinistö.
The photograph shows two women kissing while covering their naked breasts with a sign with "Finland" inscribed on it.
Videos published last week showing Marin dancing with friends at a private event led to questions about whether she had taken drugs.
She rejected all the allegations and underwent a test, which turned up negative on Monday.
Asked at the press conference whether national security could have been compromised during the night in question, Niinistö said: "I don't believe that anything out of the ordinary happened that night."
