The painting of St. John of Nepomuk, in a frame made of carved acanthus, was probably created in the years 1730-1750. It is a former altar finial of currently non-existent altar from the church of St. Sebastian or an item of the previous furnishings, transferred in the 19th century. Iconography of the painting refers to the life of St. John of Nepomuk. The saint was a canon of the Collegiate Church of St. Giles in Prague. He was thrown into the river Vltava from Charles Bridge in Prague by order of Wenceslaus IV, due to refusing to disclose the seal of confession. This scene is depicted in the background of the painting in question.
Paulina Kluz, "Altar finial with the painting of St. John of Nepomuk", [in:] "The Sacred Lesser Poland Heritage", 2021, source: https://sdm.upjp2.edu.pl/en/works/altar-finial-with-the-painting-of-st-john-of-nepomuk