Step 1.
For this trick You will need your Facebook Username. If you dont have it then click here and set your Username.
OR
You can also use your Profile Id which will be on you adress bar like this "http://www.facebook.com/profile.php?id=100000464263649" . Here 100000464263649 is you Profile ID .
Step 2.
Now Copy Your FB Username or Profile Id and Open the
Example- [[satyammaheswari]] or [[100000464263649]]
This Feature of fb is just updated.. So at this point it has some limitation also like at this moment this can be only used on PC nt in mobile device.. So make sure you and your Chat buddy both using Computer to chat.. Other Wise the One who is using Mobile Device will just see the code you have written not the pic..