Tehran and the northwestern city of Tabriz were the previous hosts of the exhibit in 2016 and 2018 respectively.
Maria Dotsenko, director of the United Nations Information Centre (UNIC) in Tehran, and a number of Kermanshah provincial officials attended the opening ceremony of the showcase, the Persian service of IRNA reported on Monday.
Dotsenko asked visitors to invite their families and friends to visit the exhibit.
The Tehran branch of UNIC has selected the photos for the exhibition in collaboration with the Iranian Ministry of Foreign Affairs and the Islamic Republic of Iran News Agency (IRNA).
Among the highlights are the photos of seven UN secretary generals who have visited Iran, as well as a selection of projects implemented by the UN in Iran.
Also included are photos related to the negotiations over the Security Council Resolution 598, which was approved by Iran.
The exhibit will be running until January 20 at the Shahid Avini complex.