  Online Social Networks explode with activity whenever a crisis event takes
place. Most content generated as part of this activity is a mixture of text and
images, and is particularly useful for first responders to identify popular
topics of interest and gauge the pulse and sentiment of citizens. While
multiple researchers have used text to identify, analyze and measure themes and
public sentiment during such events, little work has explored visual themes
floating on networks in the form of images, and the sentiment inspired by them.
Given the potential of visual content for influencing users' thoughts and
emotions, we perform a large scale analysis to compare popular themes and
sentiment across images and textual content posted on Facebook during the
terror attacks that took place in Paris in 2015. Using state-of-the-art image
summarization techniques, we discovered multiple visual themes which were
popular in images, but were not identifiable through text. We uncovered
instances of misinformation and false flag (conspiracy) theories among popular
image themes, which were not prominent in user generated textual content, and
can be of particular inter- est to first responders. Our analysis also revealed
that while textual content posted after the attacks reflected negative
sentiment, images inspired positive sentiment. To the best of our knowledge,
this is the first large scale study of images posted on social networks during
a crisis event.
