Try it and see how many IPs you get...
I haven't looked into the programming required for this, as individual IPs are of no interest to me. View counts and referring URLs are about as far as I want to go.
Actually Theymos is pointing out that it's not possible anymore. bitcointalk is using image proxy which prevents any request being forwarded to the source directly from client's browser.
If you haven't notice all [img] tages are replaced like, so you will not get IP Address of the user but all requests will be coming from bitcointalk's image proxy server.
https://ip.bitcointalk.org/?u={url}
I seriously think, bitcointalk should enable Image caching on proxy server, currently it looks like caching is not enabled or used that's why we don't see any image for few [5+] seconds.