Not to stray too far off topic but if you had a still from SAW on your bedroom wall then this section (Criminal justice) could easily be applied.
Exclusion of classified films etc. .(1)
Section 63 does not apply to excluded images. .
(2)
An excluded image is an image which forms part of a series of images contained in a recording of the whole or part of a classified work. .
(3)
But such an image is not an excluded image if .
(a)
it is contained in a recording of an extract from a classified work, and .
(b)
it is of such a nature that it must reasonably be assumed to have been extracted (whether with or without other images) solely or principally for the purpose of sexual arousal.
The Criminal Justice Act you were looking at was out of date, you were looking at 2003 when they sneaked a new one through in 2008.