Public Domain Images Worth Millions for Wikipedia

When the copyright in a work expires, or when a work is offered under an open licence, anybody may use it. While the concept of the public domain is something that most people understand, its role in spurring new innovation and creativity remains under-explored. New academic research, presented at the European Policy for Intellectual Property (EPIP 2015) conference in Glasgow, organized by CREATe (Research Councils UK Copyright Centre), seeks to calculate the value of public domain illustrations and photographs for the popular online resource Wikipedia.

The study, by Professor Paul Heald, Dr. Kristofer Erickson and Professor Martin Kretschmer, finds that availability of images in the public domain has a direct influence on whether such material is added to a content page. The addition of free materials not only reduces costs but also has a measurable effect on the rate of visitors accessing that content, representing added value for society.

The study, which is forthcoming in the September issue of the Harvard Journal of Law and Technology, examines the biographical Wikipedia pages of 1700 authors and musicians spanning the 19th and 20th Centuries. Roughly half of the notable people studied did their most important work prior to 1920. Photographs or illustrations made of those creators while they were alive usually reside in the public domain, making it easier for Wikipedia contributors to include them in articles as supplementary material.

The researchers found a strong effect associated with the public domain status of an included photograph. Even though camera technology improved and became less costly over the course of the 20th Century, the study actually found that fewer recent notable people were accompanied by a photograph on Wikipedia. Less than 55% of authors born after 1890 were accompanied by a photograph on their Wikipedia page, while for authors born before 1890, this figure approaches 90%.

In order to use an image on Wikipedia, contributors must offer a copyright justification for its inclusion. The majority of images (54%) used to illustrate notable people in this study were chosen because the copyright term had expired. Wikipedia contributors are encouraged to use illustrated material from the public domain, because it means that Wikipedia can offer its content freely for commercial and non-commercial downstream uses.

Tracking the effect of illustrated materials

What is the value of illustrated material to a text-based resource such as Wikipedia? Web marketing literature suggests that images enrich online content, making it more valuable to readers. Images can increase the amount of links a page receives, and consequently improve its visibility to search engines.

The study found a measurable uplift in visitors to pages on Wikipedia that included photographs. Accounting for differences in popularity by pairing creators of similar status, the researchers found that those with an image on their Wikipedia page benefitted from an increase of between 17 and 21 per cent in traffic.

Placing a value on public domain images

The increase in traffic generated by the presence of public domain images is one way to concretely estimate the value of the public domain. Based on the widely-used estimate that a single visitor to a commercial website of Wikipedia’s popularity can be expected to generate USD 0.0053 in advertising revenue, and estimating the total increase in visitorship across Wikipedia, the authors calculate that public domain imagery represents a total commercial value of USD 33,896,638 per year.

While this is a surprisingly large figure, it only tells part of the story. The authors estimate the additional value of public domain images by using equivalent commercial image license rates. The authors also propose future research to examine the size of economic activity enabled by downstream uptake and re-use of Wikipedia content, which is itself in the public domain.


Notes for editors: ‘The Valuation of Unprotected Works:  a case study of public domain photographs on Wikipedia’ by Paul Heald, Kristofer Erickson and Martin Kretschmer is a paper presented at the European Policy for Intellectual Property (EPIP) Conference, University of Glasgow, 2-3 September 2015.  For more information visit:

Paul Heald is Richard W. and Marie L. Corman Professor of Law at the University of Illinois.

Kristofer Erickson is Lord Kelvin Adam Smith Research Fellow, CREATe (Research Councils UK Copyright Centre), School of Law, University of Glasgow.

Martin Kretschmer is Professor of Intellectual Property Law and Director of CREATe (Research Councils UK Copyright Centre), School of Law, University of Glasgow.

For further information contact the lead author Paul Heald on + (email: or the CREATe PR team (email:

New research presented at the EPIP 2015 conference will be shared on social media using the hashtag #epip2015