An <img> element has a longdesc attribute that drops the 'l' of '.html'.

as example:
https://docs.oracle.com/javase/8/docs/technotes/guides/deploy/applet_dev_guide.html
"Figure 11-1 Thread Interactions"

Warning:
URL `img_text/thread_interaction.htm'
Name `Description of Figure 11-1 follows'
Parent URL file:///var/lib/hudson/jobs/JavadocBrokenLinks/workspace/docs/technotes/guides/deploy/applet_dev_guide.html, line 178, col 1 (HTML) (CSS)
Real URL file:///var/lib/hudson/jobs/JavadocBrokenLinks/workspace/docs/technotes/guides/deploy/img_text/thread_interaction.htm


Full report
http://spb-ebola.ru.oracle.com:8080/view/JDKMonitoring/job/JavadocBrokenLinks/lastSuccessfulBuild/artifact/output.html