You need to use the .jpg link of each individual picture to post it, rather than the gallery URL.
If you see in this screenshot, the address bar where it's highlighted is the URL you need to use.
Then you just paste that URL like so
[img] your URL goes here [/img]
or to link the gallery page itself you can just paste the address (with the http:// part) and it will auto-convert to a clickable link
and you end up with this
*note: I added the spoiler to your image because it's very large, you don't get that automatically