Wikipedia is an important global resource which benefits from availability of materials in the public domain (due to copyright term expiration and open licensed material). To assess the value of the public domain to the construction of this resource, researchers studied the presence of public domain images on biographical Wikipedia pages of 1,700 authors, lyricists and composers. 
§ Pages for authors born prior to 1880 have a greater likelihood of containing an image than pages for authors born later, even though camera technology became more widespread in the 20th Century. Less than 58% of authors in the sample born after 1880 have images associated with their Wikipedia pages. 
§ Controlling for notoriety of authors using a matched-pairs technique, we found that authors’ pages with public domain images attracted 17% more visitors than pages where no image was available, reflecting the value those images contribute to the Wikipedia resource. 
§ Using commercially equivalent licence fees obtained from Corbis and Getty for images relating to the biographical sample, we suggest that one could assign a value of USD $200 million (£127 million) per year for the 1,983,609 English-language Wikipedia pages in appropriate categories estimated to contain public domain images.