Another pic found on google with words ”mexican pig mask”. Didn’t find that much information where these masks were used. The only comment I found was on another pic. They were apparently used in religious dances.
The cover art pig mask seems to have a symbol on it’s forehead. Perhaps The Orb?
One thing that was going strong in Mexico at the time (1899) was spiritualism (vs spiritism), especially the Latin American version Espiritismo. Here is some Wikipedia snippets of the both
Spiritualism:
“Spiritualism is a religion postulating the belief that spirits of the dead residing in the spirit world have both the ability and the inclination to communicate with the living. Spiritism, a branch of Spiritualism developed by Allan Kardec and today found mostly in continental Europe and Latin America, especially Brazil, has
emphasised reincarnation.”
“Spiritualism developed and reached its peak growth in membership from the 1840s to the 1920s, especially in English-speaking countries. By 1897, it was said to have more than eight million followers in the United States and Europe, mostly drawn from the middle and
upper classes.”
Beliefs
“Although various Spiritualist traditions have their own beliefs, known as Principles, there are some shared concepts:”
• A belief in spirit communication.
• A belief that the soul continues to exist after the death of the physical body.
• Personal responsibility for life circumstances.
• Even after death it is possible for the soul to learn and improve
• A belief in a God, often referred to as "Infinite Intelligence".
• The natural world considered as an expression of said intelligence.
Espiritismo
“Espiritismo, a cultural variation on Spiritism and Spiritualism, popular in Latin American nations, particularly Mexico”
“Espiritismo (Portuguese and Spanish for “Spiritism”) is the Latin American and Caribbean belief that good and evil spirits can affect health, luck and other elements of human life.”
“Espiritistas believe these beings can influence the corporeal world in various ways and that the espiritistas, in turn, can also influence the actions of the spirits.”