Posting a link in chat of your screenshot or a web page can be fun, especially when its rather long.
Here is a simple and effective way to do it.
First open the attachment and see the string you have to create in a txt file, I use Notepad. The file sits somewhere handy on my Desktop.

Usually if its a long link like a 'dropbox picture' I open a new Tab and type in tiny.cc
Then I paste my copied link into the web page and make it shorter.

http://earthobservatory.nasa.gov/IOTD/view.php?id=37575&src=eoa-iotd
becomes
http://tiny.cc/0z9qpw

Then we paste that short link into our string, add a comment which will appear in chat.

Copy the whole line and paste it into chat, your comment will appear in Blue as a clickable link.
Too easy. Then save the Desktop text file for the next time.
Take the time to see my samples in the picture, I can't paste the text in here so I made a picture.