If you want to share a file or image on the discussion board, the best way to do this is to add the files as attachments to your post. When composing a new post you will see an "Add attachments" heading with a button to select the file(s) to attach from your computer. Once the each file has uploaded 100%, click the "Submit post" button. Your instructor and other students in the course will be able to download and view the files attached to your posts on the discussion board.
As an altnerate approach, you can also paste in sharable links from services like Dropbox or Google Drive into the message you post. This is an excellent resource from dropbox on how to upload a file and create a shareable link: https://www.dropbox.com/help/167.
This article is part of a series related to course discussion boards. For more information, please also see these related support articles: