To post a picture you
just paste the web-address of the photo into you post.
1.
To get the web-address the photo has to be uploaded to PhotoBucket (which is incorporated into the forum at the bottom of the screen when you create a new post (You can also use any other web-based photo gallery like Flickr).
2. then find the
web-address of the picture at the bottom of the PhotoBucket screen or by right-clicking on the photo and looking in "properties")
3. copy and paste the web-address into your post, eg:
http://i61.photobucket.com/albums/h57/tokpisin/highway.jxg
and when you preview your post, the web-address will display the photo, like this: