This is the Altarpiece from S. Francesco dei Zoccolanti, Matelica by Carlo Crivelli. Painted in the Italian north in 1491 for a family chapel in the Franciscan church in Matelica, a small town in the Italian Marches.
The Ottoni were the local ruling family - you can see their coat of arms placed conspicuously on the bottom edge of the main panel. The location heavily influenced the altarpiece's design. It had to be tall due to the high ceiling of the chapel and there was a large window on the back wall, so it was positioned on one of the side walls.
The painting is approximately 2.5 metres high, including the frame and predella, which is quite unusual for its time. The light in this piece comes from the upper right, mimicking the actual light in the chapel.
You can see two saints flanking the Virgin - the scholarly Saint Jerome represents the interests of the cleric Fra Giorgio di Giacomo, while the soldier Saint Sebastian reflects those of the Ottoni family. This painting is one of only three large Renaissance altarpieces here that remain in their original frames.
Altarpiece from S. Francesco dei Zoccolanti, Matelica hangs in The National Gallery on Trafalgar Square, London — free to enter. Point your phone at any artwork there and audioguide.london plays a free audio guide in six languages — no app download needed.