"Insert Object"-popup window, click on "Temporary files"
List of files available, click on "upload"
Upload window, may need to scroll to the right
Upload window, after scrolling right (notice the "Upload button")
Now choose file from hard drive by clicking "Search", then hit "Upload"
After uploading, a preview picture appears.
Now click on "Insert link"
Back on the "compose message" field, there´s the URL (link)
Click on preview, now the image appears in full size.
Click on "Edit" to edit the message
After finished editing, click on "Post"