Two questions here - firstly, it's only an illegal image if/when a court rules on it given the grey area this is in. However, it might be considered to be prudent to not make such an image available if only for self interest reasons. There is, incidentally, a difference between a website which has a policy over how it manages and controls its own content (which is what Wikipedia does) and censorship in the control of what people can and cannot see elsewhere. There's a considerable difference between the two. Wikipedia is as a joint community venture, it is not anarchy or complete free-for-all and never has been. The author of this piece ought to be able to tell the difference.
However, the second issue is El Reg's provision of a direct link to the offending Wikipedia page. that surely is inviting readers to go and look at such an image (and maybe making them liable to legal sanction).