Also it depends on what you use it for - obviously if you are going to sell t-shirts with your fresh, mint vectorized trace of Dirk the Daring, then yes I'd say that's illegal.
Well, as everybody says, IANAL, but lets think about this a bit more clearly. Lets be clear that strictly speaking the "use" which you make of an image might be relevant for a whole lot of reasons.
There's trademarks, in which case if you wrongfully use someone's trademarked image (say an image of a Street Fighter marquee, assuming Capcom have registered a trademark for this) then you are infringing their trademark and legal sanctions apply.
Similarly for copyright - if you make a copy (and lets assume for the sake of the argument that tracing an image is in fact making a copy, because this is essentially anallagous to, for example, forging a painting by "re-producing" it, even though it is not an exact digital copy).
Whether your purpose in making such a copy, or using such trademark, is a commercial one (i.e. making money) will go more to the amount of damages that a successful claimant might get, rather than whether what you have done is wrong.
That said, there is, as another post mentioned, the "fair use" loophole. This of course depends on where you are - I understand that in the US there is a stronger "fair use" argument than, for example, in Australia (where I am). Is it really "fair use" to splash a proprietary image on the side of our cabs? Probably a question for those wiser than I.
In the final analysis, I agree that it is unlikely that any company would bother to litigate this, at least not without a "cease and desist" letter first. That is of course not to say that a company couldn't do so if they chose.
Anyone who might be making and selling cabs using this sort of artwork should probably think about this pretty carefully, and maybe actually speak to a real copyright/intellectual property lawyer.
Just my 2 cents
