OWA not working and showing red Xs instead of the images?

it is possible for the IUSR anonymous auth account password to get out of sync between where its held in AD and the metabase

you can test this by unchecking anonymous auth on default website and exchweb and enabling IWA

 stop and start the default website

does IWA auth work with OWA?

 

if so the password for anonymous auth are out of sync

 https://support.microsoft.com/kb/297989 helps getting them back in sync