  Though images are ubiquitous across Wikipedia, it is not obvious that the
image choices optimally support learning. When well selected, images can
enhance learning by dual coding, complementing, or supporting articles. When
chosen poorly, images can mislead, distract, and confuse. We developed a large
dataset containing 470 questions & answers to 94 Wikipedia articles with images
on a wide range of topics. Through an online experiment (n=704), we determined
whether the images displayed alongside the text of the article are effective in
helping readers understand and learn. For certain tasks, such as learning to
identify targets visually (e.g., "which of these pictures is a gujia?"),
article images significantly improve accuracy. Images did not significantly
improve general knowledge questions (e.g., "where are gujia from?"). Most
interestingly, only some images helped with visual knowledge questions (e.g.,
"what shape is a gujia?"). Using our findings, we reflect on the implications
for editors and tools to support image selection.
