Images have been fixed
Image upload (and also download) were not working for the last few hours. This has been a recurring problem but I think I have finally found the real cause so it should not happen again. Sorry for the inconvenience.
What was the real cause?
Server's system clock was out of sync (off by 20 seconds). Because of this requests to the S3 bucket were being signed incorrectly.
Test
Here:
No need to apologise. We appreciate the effort.