  Most issue tracking systems for open source software (OSS) development
include features for community members to embed visual contents, such as images
and videos, to enhance the discussion. Although playing an important role,
there is little knowledge on the characteristics of the visual contents to
support their use. To address this gap, we conducted an empirical study on the
Jupyter Notebook project. We found that more than a quarter of the issues in
the Jupyter Notebook project included visual contents. Additionally, issues
that had visual contents in the comments but not in the issue posts tended to
have a longer discussion and to involve a larger number of discussants. In our
qualitative analysis, we identified eight types of visual contents in our
sample, with about 60% including screenshots or mockups of the main product. We
also found that visual contents served diverse purposes, touching both problem
and solution spaces of the issues. Our effort serves as an important step
towards a comprehensive understanding of the characteristics of visual contents
in OSS issue discussions. Our results provided several design implications for
issue tracking systems to better facilitate the use of visual contents.
