Triangle

Triangle is a 2009 South Korean-Japanese comedy film starring Ahn Jae-wook, Kang Hye-jung and Lee Soo-kyung. A tense standoff between a wealthy young widow with a collection of world-famous art, a swindler with an eye on her collection, and a strange woman who blackmails him into including her in the con.

Synopsis from Wikipedia, CC BY-SA 4.0. Everything below written here.

Poster © the film's rights holders.