Charity auctions & sales tax?

[Terri Ficenec]

This may be a really stupid question, but. . .
If you donate a small painting, say a head & shoulders portrait, to a charity auction, would you need to collect sales tax on the value of the painting when it is ultimately delivered? (Or is there none since you are not otherwise receiving cash for the portrait?)

I'm assuming that if the painting is upgraded, you would just collect tax on the portion that they pay you?

Or does this differ by state???