Forgent Networks is trying to enforce what it claims is its patent rights over the jpeg file format - the de facto compression method for electronic photographic images.

The company has sued 31 companies - including some of the largest IT companies in the world - and hope to extract payment before patent number 4,698,672 expires in October this year. Apple, Dell, Kodak, HP, IBM, Macromedia and Xerox are among the giants mentioned in the lawsuit.

Forgent first put claim to an element of the jpeg compression technique with its "Coding system for reducing redundancy" patent in July 2002, which was promptly dimissed by the JPEG Committee as having no foundation and effectively redundant due to prior art.

However, the company could smell money and has attempted to follow the path followed by Unisys over the other main image format - GIF. Unisys decided in December 1994 to go back on a promise made years earlier and start charging royalties on its GIF image format. It pressured companies producing software that saved images in the format to pay it royalties. And many large companies paid millions in response - despite the fact that the patent had been unenforced since 1985. The patent expired in June 2003 but not before it had sparked the creation of a rival, free image format called PNG.

Forgent has had some success though when it persuaded Sony to pay it $16 million to allow it to use the format. Since then it has pressed the issue and received around $90 million from a variety of companies. With the patent due to expire this year however, it has decided to go for the big boys and a last-ditch effort to extract as much money for its patent as it can. It is seeking damages and an injunction against the companies.

The company's CEO, Richard Snyder, said in a press statement: "Forgent is committed to developing all of its assets and technologies to maximize shareholder value. We believe we will prevail in this litigation as the '672 Patent is valid, enforceable and infringed, It's unfortunate that despite the many opportunities these companies have had to license the patent, they have all declined to participate, leaving us no alternative but to litigate."

Interestingly, Microsoft is not included in the lawsuit, leading to speculation that it is planning to pay off Forgent in keeping with its recent policy of settling long-term patent disputes.

So far all the companies named in the lawsuit are keeping mum about their intentions.