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Twitter has added photo-sharing features to its mobile service, allowing users to edit images and enhance them with artistic filters.

The features are similar to those of photo app Instagram, which stopped users from displaying its pictures on Twitter over the weekend.

Users can now only post a link to Instagram's site.

One expert said the action was designed to help the social networks make more money from their users.

Twitter explained its move , saying that users would now be able "to edit and refine photos, right from Twitter".

"Every day, millions of people come to Twitter to connect with the things they care about and find out what's happening around the world.

"As one of the most compelling forms of self-expression, photos have long been an important part of these experiences."

Removing integration

Instagram was bought by Facebook in April 2012 and has more than 100 million users.

It stopped supporting Twitter's Cards feature last week.

The facility used to ensure that images taken with the photo app and shared on Twitter were displayed in people's feeds.

But over the weekend, it became impossible to integrate Instagram photos in tweets; the only way to share one now is by posting a link taking users to the Facebook-owned site.

In a statement, Instagram's chief executive Kevin Systrom said it was done to encourage people to use his website.

"[Users can] engage with Instagram content through likes, comments and hashtags," he said.

"Now we believe the best experience is for us to link back to where the content lives."

Advertising revenue

One social media expert told the ����ý that the tit-for-tat action had been motivated by Instagram's desire to make money.

"It's all about holding on to users, preventing them from spending too much time on rival social networks," said Mark Little, principal analyst at Ovum.

"[It's all about] potential eyeballs for advertising revenues.

"So it's interesting that this partnership that built up in the earlier days and benefited both parties was never permanent - because once they gain enough benefits from each other it becomes more like rivalry.

"The next step is to get enough subscribers and to monetise them, to start defending their ecosystem from the past partners to stop themselves from losing users."

He added that since the integration between Instagram and Twitter was very popular among users, it now remained to be seen whether Facebook would introduce a Twitter-like functionality of its own.

Flickr filters

Following in its rival's footsteps, photo-sharing service Flickr - which is owned by Yahoo - launched its own photo filtering service on Wednesday.

A new version of its iPhone app contains 16 filters to alter the look of uploaded pictures.

When compared to Instagram and Twitter, Flickr is a veteran of social networking.

But while still a popular destination, particularly for serious photography enthusiasts, it has lost more casual users to the likes of Facebook.

Flickr was bought by Yahoo in 2005 for a reported $35m (£22m).