Frauds have been something of a "preoccupation" with artists and collectors, probably for about as long as there has been art and collecting. Antique collectors of all kinds run into fraudulent articles quite frequently; and it's "sort of" interesting that often known frauds are of considerable value (or at least noteworthy price).

From an essay on Why David Hockney should not be taken seriously by Brian Yoder (a rather long piece, and the quote is well down):

The Han van Meegeren Case

In the mid-20th century a Dutch artist was caught selling very high quality forgeries of (supposedly unknown) Vermeer paintings. He had great success at getting these paintings authenticated for years even though he painted them himself. In his court case where he stood accused of collaborating with the Nazis by selling them "cultural treasures," in his defense he proved that he had forged the paintings he sold to high Nazi officials by demonstrating his ability to make fake "Vermeers" before the court

An after-the-fact narration on the trial may be seen at http://www.alamut.com/proj/87/dayOfTrial.html.

The painting that van Meegeren sold to Hermann Goering as a Vermeer was titled " Christ and the Adultress," painted in 1941, an inset in the article at the above link.

(One may respect the talent of a forger like van Meegeren, but Hockney (from the Yoder article) commits a repugnant fraud simply by representing himself as being an artist. IMO.)

As to forgery by relatives:

Another purported fraud apparently not widely known is the charge made that Picasso, in his early years, forged his own name to paintings and sketches made by his father, in order to create a portfolio that would gain him admission to the art academies. (He didn't last long at the academies.) There has been some debate over whether Picasso actually could draw, and these early works have been frequently cited as proof that he could, but just didn't choose to. If the forgery charge is given credibility, along with a few other bits of evidence, he probably really wasn't particularly "competent," although a very few later works would suggest that he wasn't completely incompetent – at an advanced high school level perhaps.. See La infancia fraudulenta de Picasso for the case. The site is, unfortunately not in English, and a Google translation wasn't particularly helpful, so I had to resort to dictionaries; but I think I got the essence of the claims.

Picasso in his younger days used his given name Pablo Ruiz, and the drawings/paintings submitted were all signed "P Ruiz." His father, Jose Ruiz signed his "J Ruiz." All the "P Ruiz" signatures cited show a conspicuous "hook" at the bottom of the "P" that likely was the result of Pablo adding the top loop to a pre-existing "J." Judge for yourself, if interested.

Even if the charge against Picasso is true, the "forged Pablos" most likely would sell at prices far beyond what the originals would have drawn attributed to Jose.

John