@Dinesh Kanivu - It must only be the URL in the message, nothing else.
Otherwise, that is more than likely a result of the URL not ending in an image format.
There's no difference; if you post a link on a line by itself (it must be by itself, however) it's automatically oneboxed.
In the case of image links, that means displaying the image instead of the link.
Unlike any other chat where something is always missing. The rules are pretty understandable Overall this Antichat deserves a five star.