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Eastman Kodak Co. started shopping around its digital-imaging patents last summer, but didn’t manage to make a sale in time to avoid a bankruptcy filing. It’s now set to sell the patents under the bankruptcy proceedings.

Though best known for film-based photography, Kodak created some of the first digital cameras. At a time when cameras now go into every phone, Kodak’s patents could be worth $2 billion to $3 billion, according to various estimates. Last fall, investors valued the entire company at just over $1 billion, including its debts.

Patents may also represent a big part of the value of Research In Motion Ltd., the struggling maker of the BlackBerry. The company has seen a steep slide in sales, which has pulled its market capitalization down to $6.8 billion. Its patents could be worth $2 billion to $4 billion, analysts say.

Yahoo Inc., like AOL an Internet pioneer, has valuable patents and an ailing business as well. But its straits are not as dire as Kodak’s and RIM’s. Still, Yahoo chose to wield its patents in March, suing Facebook for infringement on 10 patents. As is customary, Facebook retaliated with its own patent suit against Yahoo, shortly after acquiring the patents from IBM.

The recent trend doesn’t mean that patents are on an unstoppable rise in value. Ferragu, the Sanford Bernstein analyst, believes that the smartphone fight is heading for a truce, where a “gentleman’s club” of companies figure out the relative strengths of their patent portfolios and work out royalty rates in accordance.

But patents are likely to keep driving deals.

“Patents are a very important asset class that have been ignored way too long,” says Alexander Poltorak, CEO of patent-management firm General Patent Corp. “Patents are the currency of the knowledge-based economy.”