Twitter Inc. unveiled tools to adjust the color, size and style of photos uploaded via applications for Apple Inc. iPhones and Android phones, as the social-media site adds features to compete with Facebook Inc.'s Instagram.

The photo filters, developed in partnership with software maker Aviary Inc., are part of an update to the mobile apps made available Mondayday, San Francisco-based Twitter said in a blog post.

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Twitter is letting users add pictures, video and audio to their postings as it steps up competition with Facebook, which bought photo-sharing service Instagram earlier this year. Last week, Instagram disabled a feature called Twitter cards for showcasing photos and other media. The move was seen as a step that better prepares Instagram for generating revenue from its own services by driving traffic to its website.

Twitter's updated photo-enhancing apps will probably bring more exposure to Aviary, a New York-based startup with backing from Amazon.com Inc. founder Jeff Bezos and LinkedIn Corp. co- founder Reid Hoffman.