I'm familiar with some situations in which artists have tried to donate art to some museum or other entity and have been told that they'd have to get the work catalogued and formally appraised. If the artist has no track record of earning $25,000 for a painting, he can't claim a $25,000 deduction for contributing one of his paintings to a museum. In many cases the museum will turn down the donation unless the artist is a person of tremendous prominence. Most of them have a lot more art than they can display and there are millions of deluded idiots churning out millions of pieces of graphic garbage they consider "art", so the standard is pretty high.
That's interesting, thanks for the info. It does seem as if the track record would be one of the defining factors, as I'm sure it is even for work done by the old masters.