The postcard shows another painting by Lourdes Oben Santos. The painting in the postcard is entitled St. Lorenzo Ruiz and Companion Martyrs. The back of the postcard mentions some information about the painting, but not if it's in a private collection or museum:
Oil on canvas
The postcard shows the kneeling Saint Lorenzo Ruiz, the first Filipino saint, Dominican Catholic priests and Japanese Catholics. At the top left part of the painting is the tsurushi.
Lorenzo Ruiz, who was falsely accused of killing a Spaniard, sought asylum on board a ship that left for Japan. The boat landed at Okinawa and the group was arrest and persecuted because of their Christian religion, and were brought to Nagasaki. On September 27, 1637, Ruiz and his companions were taken to the "Mountain of Martyrs", where they were hung upside down into a pit known as horca y hoya, or tsurushi (hence it can be seen on the postcard). Two days after, Ruiz died from hemorrhage and suffocation. His body was cremated and his ashes were thrown into the sea.
Lorenzo Ruiz was beatified in Manila on February 18, 1981 by Pope John Paul II during his Papal visit to Manila. San Lorenzo Ruiz was elevated to Sainthood and canonized by Pope John Paul II in the Vatican City, Rome on October 18, 1987 making him the first Filipino saint and the first Filipino martyr.
Lorenzo Ruiz Wikipedia Entry