Why is this photograph a primary source?

Photographs are a very common type of primary source. They can serve to document: events or relationships in a person's life. the history of an organization, institution, municipality, country, or social group

Explanation:

the  wilmot proviso  was designed to eliminate  slavery  within the  landacquired as a result of the mexican war (1846-48). fearing the addition of a pro-slave territory, pennsylvania congressman david  wilmot proposedhis amendment to the bill.

the exodus of these people from constantinople contributed to the revival of greek and roman studies, which led to the development of the renaissance in humanism and science. byzantine emigrants also brought to western europe the better preserved and accumulated knowledge of their own greek civilization