To identify the purpose of the photograph taken by Dorothea Lange, it would be most helpful for a historian to conduct more research on the lives of Florence Owens Thompson and her children.
The photograph in question is known as "Migrant Mother" and has become an iconic representation of the Great Depression.
Understanding the context of Florence Owens Thompson's life and the challenges faced by migrant workers during the Great Depression would provide insights into the purpose of the photograph. Lange's work, commissioned by the Resettlement Administration, aimed to document the living conditions and struggles of migrant workers, particularly during the Dust Bowl era.