Images assembled by Anne S. Goodrich (1895–2005) in 1931, and donated to the C. V. Starr East Asian Library, Columbia University.
The images were either purchased to be burned immediately and serve as emissaries to heaven; or purchased to be displayed for a year while offering protection to the family in a variety of ways, before being burned. The images are further divided by display locations and by the deities they represent.
"This project aims to locate, digitalize, archive, and disseminate online photographs from the substantial holdings of images of modern China held mostly in private hands outside the country. These are often of even greater historic interest than might ordinarily be the case, as the destruction of materials in China through war and revolution in the twentieth century, and especially during the 1966-69 Cultural Revolution, means that there is a relative dearth today of accessible photographic records in China itself."
2012 report by the Pew Research Center. The report quotes anthropologist Tik-sang Liu: "for ordinary people in Hong Kong and Macau, 'there is no clear boundary between Buddhism, Daoism and local [folk] religious practice.'” Also, " though folk religions are pervasive in China, they typically do not appear in surveys in China because they are not one of the five religions officially recognized by the government."
Aug. 23, 2015 article from Business Insider, focused mainly on Christianity in china. Contrast the map, and the attitude towards Christianity displayed in this article with those in Wikiwand. Note the sources for the map and accompanying graph, and that they are different for each image.