This article is part of a series related to course discussion boards. For more information, please also see these related support articles:
If you want to share a file or image on the discussion board, the best way to do this is to upload the file to a service like dropbox, then created a shareable link from dropbox and place that link in your message.
This is an excellent resource from dropbox on how to upload a file and create a shareable link: https://www.dropbox.com/help/167
Once you have created your link, simply paste the link in your post or reply on the discussion board and it will be automatically converted to a clickable hyperlink. Other students can then click that link to access your file.