This is an intended security measure. We do not want attachments to be publicly accessible as they may sometimes contain sensitive information. The files should be only accessible by the development team and the ticket's author. Who are really the only people who need access to them. They were accessible for a brief period of time in the past week or so due to an oversight in user privileges.

If you want to make the images publicly visible, upload them to an image sharing website and post a link to them.

Cheers!