1. copy the link of the picture of your choice
2. paste your link
3. before the link place[.img]
4. after the link place[./img]
5. Click preview to see if you did it correctly.
Also be sure your picture isn't to big or it will be cut off. Also rid of the dot in step 2 and 3
that should be it.
here's the a picture I used for example using these exact instructions.