Ex-Votos

Ex-votos are paintings of religious images placed in a church or chapel to express gratitude for a miracle or favor.  It was a tradition brought to Mexico by the Spanish.  As per Wikipedia...

"As in Europe, votive paintings began as static images of saints or other religious figures which were then donated to a church. Later, narrative images, telling the personal story of a miracle or favor received appeared. These paintings were first produced by the wealthy and often on canvas; however, as sheets of tin became affordable, lower classes began to have these painted on this medium. The narrative version on metal sheets is now the traditional and representative form of votive paintings, although modern works can be executed on paper or any other medium.

Narrative votive paintings can be found by the thousands in many locations in Mexico although certain shrines and sanctuaries ...attract a very large number of these. Due their proliferation, especially in the 18th and 19th century, many older votive paintings have left the places they were deposited and found their way into public and private collections. The collecting of these was begun by Diego Rivera, whose work, along with those of a number of other painters past and present, has been influenced by them. Frida Kahlo's beautiful collection of ex votes is on public display in her family home, which she later shared with Rivera, her husband."