This leads me to the ethical question, is it right for computer technicians to search customers hard drives for pictures? Where do you draw the line? Clearly in this case someone has run a deep search in unallocated space.
Is the invasion of privacy worth it if you catch paedophiles?
If they're digging around beyond the scope of the job they're doing, then I'd have to ask WTF they're about.
If they're trying to clear out some malware and are rooting around in the browser settings where they happen across a cookie or cached images, then I'd be inclined to say bang to rights.