http://3dboys2bghyeevf7j5smxtceojykpdqynuppxjvpkw23l34h3ipyduid.onion/app.php/help/faq
If the administrator has allowed attachments, you may be able to upload the image to the board. Otherwise, you must link to an image stored on a publicly accessible web server, e.g. http://www.example.com/my-picture.gif. You cannot link to pictures stored on your own PC (unless it is a publicly accessible server) nor images stored behind authentication mechanisms, e.g. hotmail or yahoo mailboxes, password protected sites, etc.