Insert the image by clicking on the insert image icon(or press ctrl+p). Once the image has been inserted click it. A pop-up menu will appear below it, and at the right side you will see the insert link option. Enter the url of the thread you want the image to forward to. And you're done.
Thanks a lot guys!Here is the bb-code if you want to do it manually.
[url=url you want]image you want[/url]