Three private equity firms, including Carlyle Group LP (CG.O) and CVC Capital Partners CVC.UL, are weighing final bids for Getty Images, as the auction of the digital media company enters its last leg, according to people familiar with the matter.

TPG Capital TPG.UL also remains in the auction and is considering a final bid for Getty, the people said. The largest supplier of stock photos, video and other digital content could be valued at as much as $4 billion, they said.

Final bids for Getty Images are due on August 6, they added.

Other buyout firms that had earlier taken a look, such as KKR & Co (KKR.N) and Charterhouse CHCAP.UL, have dropped out of the process, the people said.

A sale would come more than four years after private equity firm Hellman & Friedman LLC bought a majority stake in Getty in a $2.4 billion deal.

All the buyout firms declined to comment. Representatives for Hellman & Friedman and Getty did not have any immediate comment.

A potential deal for Getty Images underscores robust appetite for secondary buyouts - sales from one private equity firm to another - as the industry is flush with capital it is looking to put to work, and the initial public offering market remains choppy.

Since the 2008 buyout, Getty has grown earnings through more acquisitions and the company could fetch $3.5 billion to $4 billion in a sale, three of the people said.

The business has also enjoyed increasing demand for its online imagery products and services, and this could lead to Getty fetching a higher valuation multiple, they said.

Hellman has tapped Goldman Sachs Group Inc (GS.N) and JPMorgan Chase & Co (JPM.N) to examine a possible sale or public offering, sources told Reuters in May.

In March, Hellman and the company's minority shareholders reaped a $379 million dividend from Getty funded with debt and $115 million of cash. This followed a $504 million dividend at the end of 2010.

In credit notes in March, ratings agency Moody's Investors Service said Getty's latest dividend recapitalization led to a "moderately high" debt-to-EBITDA leverage of 4.4 times compared to 3.5 times pre-dividend. Getty had revenues of about $945 million in 2011.

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