Dec 20 - Instagram, the popular photo-sharing service, has retreated from some but not all of the controversial changes in its terms of service that prompted a fierce backlash from users earlier this week.

In a blog post on Thursday, Instagram founder and CEO Kevin Systrom apologized for a failure to “communicate our intentions clearly.” The terms of service changes pertaining to advertising have been reversed, Systrom said, and restored to what they had been before the changes announced on Monday.

Instagram, which allows people to add filters and effects to photos and share them easily on the Internet, was acquired by Facebook earlier this year for $715 million. Some top users of Instagram, including National Geographic magazine, said they would stop using the service after the new rules were announced on Monday.

Language that had appeared to allow Instagram advertisers to display user photos without compensation have been removed from updated terms of service posted on Thursday.

The updated terms also do not appear to contain a controversial provision which had stated that if a child under the age of 18 used the service, it implied his or her parent had tacitly agreed to Instagram's terms.

However, the new terms still contain a mandatory arbitration clause, which is not included in terms of service for other leading social media companies like Twitter, Google, YouTube or even Facebook itself. That immunizes Instagram from many forms of liability, according to legal experts.

Internet experts said Instagram had been very aggressive in asserting its rights to user information and inviting anyone who did not agree to delete their accounts within a few weeks.

The updated terms still say that anyone who accesses Instagram agrees to be bound by the new terms which are slated to go into effect on January 19. Also, Instagram kept language which gave it the ability to place ads in conjunction with user content, and “that we may not always identify paid services, sponsored content, or commercial communications as such.”

Instagram representatives could not immediately be reached for comment.

Systrom stressed in the blog post that the company had no intention of selling the photos that users post on the service. Many users had read the new terms of service as an indication that the company was reserving the right to do that.

“Going forward, rather than obtain permission from you to introduce possible advertising products we have not yet developed, we are going to take the time to complete our plans, and then come back to our users and explain how we would like for our advertising business to work,” Systrom said.