Primary image?

My primary image is showing the filename, which looks quite ugly. Is there a way to stop this?

Assuming you haven't modified your theme at all, it sounds like Omeka didn't create a derivative file for your image. Do you see the filename in other places, like in the admin page for your item?

No, if I click on edit image the name of the file is in the name section just under dublin core, I have made the exibit public so you can look at what I mean.