I do not know why the images are no longer available in the original post, but anyone can find them in the archived version:
Could be a number of reasons:
- The service or the account where they were originally hosted is no longer available. The link says "dropboxusercontent.com". Maybe it's an older version of Dropbox.
- The images are still there, but the links have changed. bitboy never posted the new ones.
- The forum no longer allows images from that particular source similarly to how some other image hosts no longer work on Bitcointalk.