The popular online hangout MySpace has blocked parts of Photobucket, complaining that the Web hosting service has been encouraging users to incorporate an ad-supported slideshow into their MySpace personal profile pages.

MySpace says it has blocked video and slideshows, though Photobucket says the block affects video only; The Associated Press confirmed that some slideshows were viewable Wednesday.

Both companies say still images are not affected by the blockage, which News Corp.'s (NWS) MySpace described as a response to violations of its policies banning unauthorized commercial activities.

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MySpace users often embed third-party photos, video and other material in their profile pages, and sites like Photobucket and Google Inc.'s (GOOG) YouTube make that easy by providing the programming code to cut and paste into the MySpace pages.

The practice has made Photobucket one of the leading sites on the Internet, even though relatively few access content directly through its home page.

The block, which began Tuesday, led Photobucket Chief Executive Alex Welch to accuse MySpace of limiting free expression and treating users as a commodity.

"They've always been about self-expression, and now they are cutting users off from doing that," Welch said.

In a statement, MySpace said it encourages users to embed third-party materials as long as they comply with the site's terms of service.

Although MySpace's complaint is over a slideshow promoting the upcoming "Spider-Man" movie, the company could identify and block only the Web address for all video and slideshows, including those that comply with the MySpace policies.

MySpace has blocked third-party content from time to time, leading to complaints that the site was trying to inhibit potential competitors as it begins to offer its own services like video. But MySpace usually cites a policy violation, a technical glitch or a security issue in justifying the block.

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