Images, such as build icons, start disappearing sporadically from the Jenkins UI. The UI instead displays a "broken image" icon. When accessing the image's URL, such as e.g. http://<jenkins-host>:6080/static/cc7624e2/images/32x32/health-00to19.png, a 404 error is returned.
The images appear to be served from the /tmp/jetty-0.0.0.0-6080-jenkins.war-
any/webapp/images/ folder. By default, CentOS runs a daily cron of tmpwatch, which deletes files under /tmp that haven't been accessed in 10 days. So image files are deleted if Jenkins is running for more than 10 days, and an image hasn't been accessed (for example, the health-00to19.png won't be accessed if there were no builds with <20% health lately).
I was able to resolve the problem by editing /etc/sysconfig/jenkins and adding " -Djava.io.tmpdir=/var/tmp" to JENKINS_JAVA_OPTIONS. However, it would be better if Jenkins came correctly configured out-of-the-box.