But instead of making the 10-minute trip to the gallery, she logged onto Amazon Art, a fine-arts and collectibles category that Amazon introduced on Aug. 6. She clicked on images by Ms. Wood, selected a pen-and-ink drawing of an unearthed plant root titled “Excavated” and, with a few clicks of the mouse, bought it for $160.

“I bought it through Amazon because it was quick and easy,” she said.

Amazon is betting that millions of buyers like Ms. DeFord will happily buy paintings and prints in the same way that they now buy shoes or books or kitchen appliances online. To entice them, it conducted a far-reaching art dragnet, approaching galleries in the United States and a few foreign countries with a simple proposition: put your work on our site and, for a percentage commission on each sale, we will expose you to our 100 million customers in North America and 200 million customers worldwide.

Because Amazon does not disclose sales figures, it is unclear whether this gamble is paying off.  Kate Nielsen, a Brooklyn artist, got the call in July. Someone at Amazon had seen her Web site, mistakenly assumed that she was a gallery owner, and asked her to sign up. “It’s such a monster company, it was disconcerting,” Ms. Nielsen said. “I thought, ‘How did you find me, this little person in Brooklyn?’ ”
To date, the company has signed up more than 180 galleries and offers more than 43,000 two-dimensional works from about 4,500 artists, ranging from “Untitled (Dollar Bill),” by Ryan Humphrey of Queens, selling for $10, to Monet’s 1868 portrait of his son Jean ($1.4 million), and, at the top of this very big heap, Norman Rockwell’s 1941 painting “Willie Gillis: Package From Home” ($4.85 million). Ms. Nielsen offered several of her digital prints for $45 each.

The Monet and the Rockwell proved to be catnip for the news media and targets for snide remarks, many of them on Amazon’s Web site. The economist and critic Tyler Cowen (a regular contributor to The New York Times), appraising Amazon’s higher-priced wares on his blog, Marginal Revolution, wrote: “I’ve browsed the ‘above 10k’ category, and virtually all of it seems a) aesthetically abysmal and b) drastically overpriced. It looks like dealers trying to unload unwanted, hard-to-sell inventory at sucker prices.”
The company did not create Amazon Art to sell Impressionist masterpieces. As its representatives were quick to point out, 95 percent of the works offered cost less than $10,000. About a third of them cost between $250 and $1,000.

Some dealers put just a handful of images online. Most have a few hundred. RoGallery, in Long Island City, Queens, has more than 6,000 images on Amazon Art. Ugallery, in San Francisco, and Zatista, in Philadelphia, two of the best-known online galleries, have more than 4,000 each.
Sellers pay a commission that starts at 20 percent for works up to $100, and decreases to 5 percent for works over $5,000. Some pass the cost on to their artists; others do not. Customers wary of fraud must rely on the reputation of the galleries, and on Amazon’s longstanding policy of allowing its customers to return merchandise within 30 days for any reason.

Amazon makes no claims about the quality and imposes no taste criteria. “We are not doing any curation,” Peter Faricy, Amazon’s vice president and general manager of Amazon Marketplace, said in a recent interview. “We look to the galleries for that.”

Mr. Faricy called the sellers on Amazon Art “the most well-regarded and reputable galleries in the world.” With few exceptions, however, the names ring no bells. There is no Pace, no Gagosian. The list runs to galleries like Masterworks Fine Art in Oakland, Calif.; Edgewater Gallery in Middlebury, Vt.; and Borghi Fine Art in Englewood, N.J.