Twitter's filters mimic the popular feature that has defined Instagram, the booming photo service acquired by Facebook this year for $715 million.

Although the new filters represent a modest product announcement affecting a small slice of Twitter's overall user experience, the move carries symbolic weight in the escalating battle between Facebook and Twitter for dominance in the social media sector.

Twitter's new release came days after Instagram unexpectedly said it would no longer allow Twitter to display Instagram photos within Twitter messages. The reason, Instagram CEO Kevin Systrom said, was to drive visitors to Instagram's own website.

Although Systrom told Reuters last week he had no specific plans to disclose how he plans to monetize his service, analysts say Instagram would be a rich vein of advertising revenue for Facebook when, not if, the world's No 1 social network decides to tap it.

Twitter said its new features are powered by Aviary, a New York-based company that develops image-editing software for photo-sharing platforms like Flickr, among others.

Since social networks began supporting photo integration in recent years, the medium has proved massively popular to users, while video-sharing, for instance, has not quite caught on.

Bijan Sabet, an early Twitter investor, said the emotive quality of photos were on display on election night in November, when an image of President Obama hugging his wife Michelle sent the moment he claimed victory, broke the record as the most widely circulated tweet of all time.

"From ordinary life to these special moments with artists, celebrities, or politicians, photos have always been this special thing for Twitter," said Sabet, a partner at Spark Capital, the Boston venture capital firm that also holds a stake in Aviary and brought the two companies together for the partnership talks.

Facebook CEO Mark Zuckerberg similarly argued for the importance of photo-sharing when he shocked Silicon Valley earlier this year by making an offer to Instagram valued at the time at $1 billion.

"Providing the best photo sharing experience is one reason why so many people love Facebook and we knew it would be worth bringing these two companies together," he wrote in a Facebook post justifying the deal.

Twitter's new photo effects will be incorporated as part of an update to the Twitter's iPhone and Android apps, available beginning Monday, the company said.

(Reporting By Gerry Shih; Editing by Bernard Orr)

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