This is easier to do than to explain, intended to help people who join a forum for the first time.
First it's a good idea to get a free Photobucket account photobucket.com/ which lets you upload pictures.
Upload the images.
The snapshot below shows one of my Photobucket pages.
By clicking below the SPIDER cover image, I selected the code needed to hotlink it to a board - you can see it highlighted blue.
You copy the highlighted code by pressing CONTROL-C.
Then when you're making your post at the Vault, press CONTROL-V to paste the code in.
You can immediately check it by previewing your post.
Tip: You can view any 'code' used in posts by logging in and pressing the 'quote' button for the post. My image links to Flickr (another image hosting site) are a little different to comply with their requirements.
Hope this helps. Like I said, easier to do than to explain.