NEW YORK - Instagram, the photo-sharing service, said it will revise a planned update to its service agreement after confusion about its intent led to widespread user complaints Tuesday.

At issue was whether users' photos can be part of advertisements, on and off Instagram. The company said in a blog post that it had no plans to put users' photos in advertisements.

That said, Instagram maintains that it was created to become a business and would like to experiment with various forms of advertisements to make money. The new policy will take effect Jan. 16.

The updated terms of service say users agree that their photos could be used "in connection with paid or sponsored content." The current terms say the service can place ads "on, about or in conjunction with your content."

The fast-growing site is a popular way to share photos from cellphones. Facebook Inc. bought Instagram in September. The cash-and-stock deal was worth $1 billion when it was announced in April, though that fell to about $740 million by the time it was completed because of Facebook's falling stock price.

The updated terms suggests that Facebook wants to integrate Instagram into its ad-serving system, which can, for instance, promote an item by telling users that their friends "Like" it. The new terms make it clearer that Instagram could use your photos to market to your friends.

In announcing the change, Instagram had said a concurrent change to the privacy policy, a separate document, would help Instagram function more easily as part of Facebook.

Twitter users were vowing to cancel their Instagram accounts in response to the policy change, complaining that the new terms would essentially let the service sell people's photos for ads.