Template images are not showing

I have just logged in this morning and noticed the static header image (company logo) that all my emails possess is not showing. When I look at previously sent emails they are also not showing.

It looks fine in edit mode, but in preview and sample the images are missing.....

Is this likely to be a temporary Marketo glitch with the image code? I know that no one has accessed this since myself on Friday!


Any suggestions???

Thank you!