As I've asserted before, stock.xchng has no legal standing to make these conditions. They are not the copyright holder, nor have they been assigned any control over it.
Their terms and conditions are nothing to do with copyright permission at all. They are a (legally dubious) contract between stock.xchng and the individual downloader ONLY, even if the terms are valid. The downloader is, notably, NOT made to apply these conditions to anyone THEY give the image to.
The stock.xchng terms and conditions do not attach themselves to the downloaded image. They attach themselves to the person who does the downloading.
Furthermore, when you upload an image to stock.xchng and make it freely redistributable, you do not state that any conditions apply. You click on a checkbox that says 'no restrictions'.
The terms of the download page form the entirety of the license between copyright holder and downloader.
Given this, I would strongly suggest that removing stock.xchng images becuase of a legally dubious "contract" that only binds the original downloader and not subsequent reusers is premature.
Having said this, it wouldn't hurt to clarify with image owners and remove all doubt.
-Matt (User:Morven)