I have had this problem for most of the time since buying a new PC and installing Office 365. Every so often there will be an update to the system and then the images reappear for a while, sometimes for a few days or a week or two, and then they disappear again. Every day I go through the palaver of going to the trust centre and ticking and then unticking the boxes, then have to restart the computer, which fixes the problem until I switch off again. Totally fed up.