When people think of a piece of art, the first thing that they generally think of is its appearance. The appearance alone is not what gives the art its value though.
If a (visually) identical copy was produced, would it have the same value as the original? In a few isolated cases it might, but generally the value comes from the story behind the piece – its provenance. Provenance has become more important in recent years, as it also defines the legality of the owner’s entitlement to the piece. How was it acquired & when was it acquired? If it can not be proved that it was originally acquired legally from a archaeological site, then the piece can not easily be traded on the open market. Institutions might want to turn a blind eye to this, but the problem is still there, as evidenced by the current troubles  faced by the Getty.
If you want to find out more about the issues associated with unprovenanced antiquities, then the journal of the Illicit Antiquities Research Centre, Culture Without Context  is one of the best places to start.
International Herald Tribune 
Beauty or provenance: Which counts more?
By Souren Melikian International Herald Tribune
SATURDAY, OCTOBER 29, 2005
LONDON Collectors of antiquities from the ancient world and the dealers who cater to their needs have been reading the writing on the wall for some time. The Unesco Unidroit convention has changed the ballgame once and for all, even if very few countries have signed it. Gone are the good old days when you bought, without asking questions, any sculpture and pot dug up from an underground cache or any fragment removed from some field of ancient ruins.
The Unesco convention, seeking to protect the heritage of mankind, may be naïve in the scope of its ambition, but it has already left its stamp on the trade in antiquities. People are becoming increasingly aware that looters going through an archaeological site destroy two-thirds of the objects and completely wipe out the unwritten historical record that a properly excavated site represents.
A cloud of suspicion now hangs over any work of art, from Sumerian tablets dating from the third millennium B.C. to late Roman sculptures, that cannot be proved to have reached Western markets before 1970. In 10 years, these artifacts will be hard to sell and their financial value will plummet.
Already, leading European institutions like the British Museum will not touch excavated antiquities of unclear provenance. More important, high-powered collectors and dealers who want to be able to sell their acquisitions, if so desired, work that factor into their calculations. Even auction houses, which used to be tolerant of human cynicism, now follow suit.
On Oct. 18, it was notable that the provenance was dutifully specified under almost every item of any significance in the catalogue that accompanied a sale of “fine antiquities” at Christie’s.
A great play was made of “The Collection of the Late Wilhelm Horn.” A bespectacled portrait of the collector was reproduced on a whole page.
Not that the items were particularly dazzling. Either Horn, a Berlin banker who, the catalogue stressed, had enjoyed both financial means and the friendship of distinguished academics, had a rotten eye, or his collection had been skimmed at some earlier time. Still, many of the works had one irreplaceable virtue. They were illustrated in the catalogue of a Berlin show held in 1938 under the title “Antiken in Deutschen Privatbesitz,” or “Antiquities from German Private Collections.” It was as if a magician had touched them with his wand.
Some modest pieces in the collection would have been doomed in a different context. You would hardly expect a Roman Venus of the second century A.D., missing one foot and most of the left arm, to set a roomful of connoisseurs on fire. The small bronze, a mere 14 centimeters, or 5½ inches, high, was not made any more attractive by a gritty surface; but it had been bought in 1936 and reproduced by Karl Anton Neugebauer in the 1938 catalogue – an effective guarantee that it met the Unesco standards. At £4,800, or $8,500, it doubled Christie’s estimate.
Another Roman Venus, lacking both arms, would have been a hard sell three decades ago. This month the small bronze brought £8,400. Call it the Neugebauer effect.
Then came the one truly good piece in the collection, a Roman marble head of a boy carved toward the end of the first century B.C. The Neugebauer certificate of legitimate ownership worked wonders. The sensitive portrait had been roughly handled by whoever cleaned the surface. But who could now resist a marble discussed by the director of a Geneva museum in a letter to Horn as early as 1930? It zoomed to £78,000.
Even third-rate Egyptian pieces in Horn’s collection were looked at with starry-eyed rapture. A bronze statuette of a god, Ptah, five inches high, managed a more than decent £10,800, followed shortly after by a bronze figure of the god Khonsu, cast in the fifth or fourth century B.C., when Egyptian society and art were in a period of deep decadence.
With its eyebrows raised in pained amazement, Khonsu seemed to wonder how the Neugebauer magic could lift its price to £10,200, despite its lack of elementary proportion and a cartoonlike appearance.
The way was now paved for the big attraction of the day, a series of marble sculptures fascinating for what they said about the 18th-century perception of Roman art.
The great and the good wanted their antiquities to be neat. A headless figure of a woman of the first century A.D., probably acquired by the third Duke of Buccleuch, touring Europe in the 1760s, was retrofitted with a curiously English-looking head, and so adorned, the statue nimbly ascended to £164,800.
The bust of an Antonine prince who lived in the second century A.D. once adorned Fawley Court, in Oxfordshire, England. The soppy expression with a wan smile could be that of an English boy bullied in his boarding school and trying to put on a brave face. Beauty is in the eyes of the beholder, and bidders sent this treasure from England’s artistic heritage soaring to £105,600.
There was more to come. Looking at the sculptures that once stood in Capesthorne Hall, the family seat of the Bromley Davenports in Cheshire, England, one felt irresistibly reminded of Bertie Wooster entering the hall of one of the aristocratic country houses immortalized in P.G. Wodehouse’s satirical novels.
A “marble head of the Roman dictator, Sulla” was effectively identified by Christie’s as an 18th-century forgery. A gullible young aristocrat on the grand tour in Italy had evidently fallen for the marble, perfectly suited to the late Georgian age. The firm lips, the frowning eyebrows, the deep wrinkles give it an air of manly dignity, much admired at the time. Sadly, it did not sell.
Other marbles that had that inimitable, slick appearance of Roman antiquities acquired by Britons in 18th-century Italy were treated with greater deference. A “Roman marble bust portrait of a man” said to date from “50-120 A.D.” seemed to share some sort of kinship with “Sulla.” Still, it pulled through, at £45,600.
So did, if at a more modest £30,000, a “Roman marble head probably of a Greek philosopher.” Were the bidders in the room reminded of the peevish faces of their schoolteachers when they failed to pay attention? Something about the realistic handling of the face looked vaguely familiar, and the folds of the drape had a softness rare in Roman sculpture, but dear to 18th-century connoisseurs. Italian restorers often did their best to oblige, if only by polishing.
A terra-cotta head of a third century B.C. youth with tearful eyes lacked the irony that marks early Etruscan work. It had the sentimental look of a portrait by Jean-Baptiste Greuze. Deeply moved, the room bid to £90,000.
Style clearly was not the issue. Indeed, the last lot could not have been more different. On a Greek amphora of the last quarter of the sixth century B.C., Hercules is seen about to slay a lion. On the opposite side, two nude satyrs seized with erotic frenzy dance around Dionysus. A dealer paid a huge £187,200 to secure the Attic black figure vase graced with a provenance guaranteeing that no one could successfully challenge the legitimacy of its ownership.
That should still leave him a substantial profit margin. Museums and international collectors are suddenly getting shy. They shun international wrangles and to do that, they will pay the earth.