I tried two ways of uploading a picture:
(1)Use the "upload" option, which says "Select local image to upload to PhysicsOverflow Server (jpeg,png,gif)"
(2)Use the "source" option, under which I need to input the URL of my image.
Neither works for me, and the same error message "Image source URL is missing" pops up, and meanwhile the option tag automatically jumps to "Image info".
At least method (2) used to work for me, but now it doesn't any more.