Thanks. I just worked it out - I had an nginx rewrite rule that was trying to get people off https when not at ^/register/ or ^/accounts/subscription/. So ima

Thanks. I just worked it out - I had an nginx rewrite rule that was trying to get people off https when not at ^/register/ or ^/accounts/subscription/. So images were requested with an https but then returned over http. I added ^/static/ to the list of requests which can be served over https and it seems to have fixed the problem. :)