Giovanni di Bartolomeo d'Aquila
The Preaching of St. John of Capistrano

Wearing the Franciscan habit and tonsure, the saint is shown preaching outside a church and holding up the sunburst symbol associated with him. At the left and right edges a man and woman are cured of demonic possession. Their affliction is expressed by the wild hair and flailing arms, and the cure by the little black demons taking flight.

The Wikimedia Commons page from which I took this image gives the artist's name as Giovanni di Bartolomeo d'Aquila. I can find no such name anywhere, but there is a 15th-century Franciscan painter of some reputation named Bartolomeo di Giovanni. Considering the 15th-century style of the image and the Franciscan connection, it seems possible that he is our man.

More of St. John of Capistrano

Source: Wikimedia Commons