We'll soon be on a new forum which has a considerably easier method for implementing images.
For now, we don't allow users to upload directly to the forum. If you wish to insert an image, upload them to somewhere like here;
http://postimage.org/
... You can then copy an paste the supplied URL or if you want to embed it, click the 'Insert Image' icon along the top an select 'From URL' an paste the URL in