Broken Images on My Website

Using version 3.5.1. I am having a problem with my images suddenly appearing broken. What is strange about it is that they don’t appear broken for everyone. One person says they are all broken, I am only seeing one broken (a social icon at the top of the page), and another person said she doesn’t see any at all that are broken.

What could be causing this? I have done the usual … deactivate plug-ins, revert to another theme, etc. and have not been able to narrow it down.