Tewell had been interested in photography since the 1950s, describing his life as "always pointing in the direction of photography," as noted in a 2017
Philippine Star feature by former Senator
Nikki Coseteng. His collection expanded to include photographs of historic sites, everyday street scenes in Manila and Cavite, significant events such as the 1928 eruption of
Mayon Volcano, and images taken during and after World War II, including the ruins of the
Old Legislative Building. Over the years, Tewell collaborated with authors, historians, collectors, and conservators, sharing images that contributed to the study of Philippine architecture and culture. Before his death, he digitized nearly 13,000 photographs, many of which were uploaded to a publicly accessible
Flickr account that has accumulated more than 60 million views as of 2026. His original prints were deposited for safekeeping at the Filipinas Heritage Library at
Ayala Museum in
Makati. The breadth of his archive spans various themes, including Spanish colonial-era Philippines, pre- and post-war Manila, traditional architecture, indigenous communities, and daily life during the 19th and early 20th centuries. ==Illness and death==