3. Upload the picture by browsing on your computer and clicking on Host it! or
If it is on the web, copy its URL into the field and click Host it!
4. Once uploaded, you can just copy the URL into the post.
On imageshack.us, you can choose if you want to show the whole picture, or just a thumbnail version of it.
For posting the picture, copy this one: Hotlink for forums (1)