The first time I came across these votives was in the Frida Kahlo Casa Azul in Mexico City. She and Diego Rivera owned over a thousand of them.
This one is dedicated to the Virgen del Carmen becasue she saved him from the spirit of his friend who appeared to him. It measures 10x12 inches. I don't know the age of this retablo.
A retablo in Mexican folk art (also lámina) is a devotional painting, especially a small popular or folk art one using iconography derived from traditional Catholic church art. Many are ex-votos ("from a vow") that depict the story that led to their commission, usually dangerous or threatening events that actually occurred, and which the person survived, thanks to the intercession of a sacred person - God, Mary or a saint. They are made as a way of thanking the sacred person for protection in precarious situations, such as surviving an illness or earthquake. This class of ex-votos often shows the protected humans in the dangerous situation, and the sacred person who protected them, usually with an inscribed explanation of the events, with the date and location. Both devotional and especially ex-voto retablos may be deposited at a shrine as a votive offering, or alternatively kept at home.