  Wikipedia is the largest source of free encyclopedic knowledge and one of the
most visited sites on the Web. To increase reader understanding of the article,
Wikipedia editors add images within the text of the article's body. However,
despite their widespread usage on web platforms and the huge volume of visual
content on Wikipedia, little is known about the importance of images in the
context of free knowledge environments. To bridge this gap, we collect data
about English Wikipedia reader interactions with images during one month and
perform the first large-scale analysis of how interactions with images happen
on Wikipedia. First, we quantify the overall engagement with images, finding
that one in 29 pageviews results in a click on at least one image, one order of
magnitude higher than interactions with other types of article content. Second,
we study what factors associate with image engagement and observe that clicks
on images occur more often in shorter articles and articles about visual arts
or transports and biographies of less well-known people. Third, we look at
interactions with Wikipedia article previews and find that images help support
reader information need when navigating through the site, especially for more
popular pages. The findings in this study deepen our understanding of the role
of images for free knowledge and provide a guide for Wikipedia editors and web
user communities to enrich the world's largest source of encyclopedic
knowledge.
