Some Instagram users are abandoning the service after the firm announced it was giving itself the right to sell people's photos to advertisers.
The Facebook-owned photo-sharing network is introducing new terms of service on January 16 which are an automatic opt-in - unless people decide to leave.
The new terms mean Instagram can share information about the people using the service with Facebook - and with its advertisers.
As well as giving itself the right to sell people's pictures, the new terms mean users will receive no payment themselves and will receive no notification about what is happening to their images.
Tech website BuzzFeed said: "There's an adage that's basically a cliche in tech now: if you are not paying for it, you're not the customer. You're the product being sold.
"Well, there's a reason that it's become cliche, and that's because it's true - over and over and over again."
Instagram users were quick to take to social media such as Twitter to voice their concern - and in some cases their outrage.
User Wardina Safiyyah tweeted: "Shud we all leave IG now? Instagram says it now has the right to sell your photos."
Fellow user maggielmcg wrote: "Bye Instagram. As of Jan they will be able to sell user's pics as stock photos with no revenue share."
John Frankel was more forthright, tweeting: "DISGUSTING: Instagram says it now has the right to sell your photos."
Wired even wrote an online article telling users How to Download Your Instagram Photos and Kill Your Account .
Instagram explained the changes in its new terms of service, saying: "Some or all of the Service may be supported by advertising revenue.
"To help us deliver interesting paid or sponsored content or promotions, you agree that a business or other entity may pay us to display your username, likeness, photos (along with any associated metadata), and/or actions you take, in connection with paid or sponsored content or promotions, without any compensation to you."
Sarah Byrt, intellectual property partner at law firm Mayer Brown, said: "Instagram may face another user backlash once people see how their photos are used.
"It makes it all the more important that users check their privacy settings. Legally, it doesn't mean Instagram can ignore other rights.
"For example, if the user had taken a picture of someone famous without their consent, or had taken a picture of something protected by copyright, Instagram - or the company using the picture in an ad - still need to think about those issues."