Free legal advice - worth the price you pay?

While we're on the subject of getting free advice (see Simon's N T hell post below), does anyone know what the legal status of pastiche and homage is?

Obviously, something like Mona Lisa is out of copyright, but what happens if you pay homage to something more recent, like a famous album cover from 1973, say?

The internet is no help, because there's a kind of moral panic about copyright issues and service providers etc. are likely to err on the side of caution, reinforcing the views of the corporate lawyers who threaten to sue fan fiction sites, lyric sites, tab sites etc.

But if you take an artwork - famous album cover, say - and change it to a large degree (replace one element with another, use slightly different colours), so that you're obviously not representing it as the original, but as a pastiche of the original, can you get sued?