The reason I picked the crucifixion is that it's so rife with symbolism, and means so many different things to so many different people, and interpretations change so radically over the ages. The Isenheim Altarpiece was once hung in a hospital to help bring relief from suffering for dying people...now, we look on it with horror, if anything, for its graphic gruesomeness.
afaict The 8 panels of the Isenheim Altarpiece were commissioned
for the church of a monastery that housed a hospice for mainly terminal victims of the plague.
Interpretation of the iconography is controversial because it isn't certain which day which panel was opened, or what purpose each stage served. The performance for which the paintings were designed has been lost, the original meaning has been lost. So interpretation of one panel, showing Christ's suffering on the Cross, as intended to produce a bond of sympathy with the suffering of the plague victims; and interpretation of another panel, showing the clean body of the Risen Christ, as intended to suggest their freedom from pain and disease in the hereafter, is speculation.
I think the fact that people take vastly different things from paintings in different times is one criterion for a serious work of [painting] art. But that doesn't really work with photographs, because while (I believe) photography is a serious art form, it is essentially different from painting. As long as people are human and use native vision, I think the meanings of photographs will remain relatively fixed -- when you think of great photographs (choose one) how will the interpretation of that work change in 100 or 200 years?
Timothy O'Sullivan's 1870s photographs of record from the Geological Exploration of the Fortieth Parallel re-interpreted as art during the 1930's and 40's.
Sebastião Salgado's 1984/5 photojournalism of the Sahel famine mostly unpublished in the US until 1990 when it was re-interpreted as art and exhibited at SFMOMA
In 100 years will anyone remain who can believe that photographs were once expected to represent a specific object in a specific place at a specific time? In 100 years will anyone understand a photograph as more than a still frame from a lost video commercial?