The case of the missing image…
Turns out this was due to my old windows credentials being cached on the tfs server credentials cache.
To fix this, I logged onto the tfs server directly via my admin account and updated the credentials there in the windows credentials manager.
Also ran fiddler in the background and cleared the winnet cache as well
Then it refresh a few times on the work item ticket back in visual studio, and hey presto they are all showing again.