is this legal?

[redregon.livejournal.com]

imagine that you've been commissioned to draw a character. you get the picture done, but the person doesn't send payment within the agreed time span... does that mean that the characters that you've been asked to draw are your property? i know the pictures would be yours, but what if you wanted to vent some frustration and draw said character in a very VERY unbecoming situation or pose... is that legal? (and yes, i know it would be bad form.)

and no, i don't want to hear the dreck about how characters that aren't actually copyrighted being copyrighted to so and so... last i heard, the "poor man's copyright" of sending an insured package to yourself is inadmissable if it's ever challenged.