I've read this article (Imagehoster Go Rewrite Announcement), and I feel that big improvements in image hosting are coming. The current steemitimages service can be used as a "file hosting" service (oops!) for any type of file if you just add an image extension, for example, a JPG. I consider this a serious security bug, and I hope no one is using it for bad purposes. But if the updated image hosting checks the file MIME type, and if images are re-converted during upload and storing on the server in that form, then this issue will be fully solved.