I've only been trying to post one image and it allows me to attach the image but when I go to either preview or post it brings up the 403 message. As an experiment I tried attaching a second image to see if that would allow the first to work, but attempting to attach a second image goes directly to the 403 message.
Images have been small (under 50Kb) and with short (6 or 7 letter file names) and all attempts both yesterday and today have failed. I get the same result attempting to edit a post or attempting to make a new post.
Michael Allen