(As far as I can tell this is not actually caused by
MBS-6673, fixing that has just made it possible to find the other bugs)
Uploading a single image now works. However things start to behave strangely if you try to upload multiple images. The discussion is at http://chatlogs.musicbrainz.org/musicbrainz/2013/2013-10/2013-10-30.html
When uploading to the real CAA, the uploader will say that the first image succeeded and then say "Error creating edit" for the second. This implies that both images were uploaded to the server and that only the first image has an edit associated with it. What actually happens is that the second image is uploaded to the server, an edit is created for the second image, but the image types used in the edit are from the first image.
Possibly relevant: When testing on a sandbox, uploading multiple images worked in Opera but in IE one image says "Error creating edit" but the other fails with "Error uploading image" and the error console says
SEC7120: Origin http://nikki.mbsandbox.org not found in Access-Control-Allow-Origin header.
SCRIPT7002: XMLHttpRequest: Network Error 0x80070005, Access is denied.