I'm not certain now if it requires a few posts before posting a picture but I think maybe you need five posts first??? Might check that part. After that it is a matter of having the pictures on an online site. I use Photobucket but there are lots of them. After the pic is on a site, you are ready to go.
Click the box above labeled IMG,
copy and paste the picture info,
Click IMG again.
Definitely do a preview to see that it all comes out correct and then submit.