My organization utilizes SharePoint 2013. Some users see an "X" instead of the image. As an admin, I can see the image. We use Windows 10. SP only displays in IE 11.
Where does the image come from? Make sure the user have permission to see the image.
To check if the issue is related to your web browser. For those who cannot see the images, use another browser and see if the issue persists.
SharePoint 2013 – Images Showing up as a Red or Black X for your reference: