Ryan Cox, a 29-year-old management consultant at ExactTarget, an Indianapolis-based interactive marketing software company, said he had already moved his photos to Flickr, Yahoo's photo-sharing app, where he could have better control.
Mr. Cox said the uproar this week over whether Instagram owned its users' photos was "a wake-up call."
"It's my fault," he continued. "I'm smart enough to know what Instagram had and what they could do -- especially the minute Facebook acquired them -- but I was a victim of naïve optimism."
"Naïve optimism" is as good a term as any for the emotion that people feel as they put their private lives onto social networks.
Companies like Google, Twitter, Yelp and Facebook offer themselves as free services for users to store and share their most intimate pictures, secrets, messages and memories. But to flourish over the long term, they need to seek new ways to market the personal data they accumulate. They must constantly push the envelope, hoping users either do not notice or do not care.
So they sell ads against the content of an e-mail, as Google does, or transform a user's likes into commercial endorsements, as Facebook does, or sell photographs of your adorable 3-year-old, which is what Instagram was accused of planning this week.
"The reality is that companies have always had to make money," said Miriam H. Wugmeister, chair of Morrison Foerster's privacy and data security group.
Even as Instagram was pulling back on its changed terms of service on Thursday night, it made clear it was only regrouping. After all, Facebook, as a publicly held corporation, must answer to Wall Street's quarterly expectations.
"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," Kevin Systrom, Instagram's youthful co-founder, wrote on the company's blog.
Instagram's actions angered many users who were already incensed over the company's decision earlier this month to cut off its integration with Twitter, a Facebook rival, making it harder for its users to share their Instagram photos on Twitter.
Users were apprehensive that the new terms of service meant that data on their favorite things would be shared with Facebook and its advertisers. Users also worried that their photos would become advertising.
Instagram is barely two years old but has 100 million users. Last spring, Facebook announced plans to buy it in a deal that was initially valued at $1 billion. The deal was closed in September for a somewhat smaller amount.
For some users, Mr. Systrom's apology and declaration that "Instagram has no intention of selling your photos, and we never did" was sufficient.
National Geographic, which suspended its account in the middle of the uproar, held a conference call with members of Facebook's legal and policy teams. Afterward, the magazine, which has 658,000 Instagram followers, said it would resurrect its account.
Also mollified was Noah Kalina, who took wedding photographs earlier this year for Mark Zuckerberg, the founder of Facebook. In a widely circulated post on Twitter, Mr. Kalina said the new terms of service were "a contract no professional or nonprofessional should ever sign." His advice: "Walk away."
On Friday, the photographer said he had walked back. "It's nice to know they listened."
Kim Kardashian, the most followed person on Instagram, said on Tuesday that she "really loved" the service -- note the past tense -- and that the new rules were not "fair." She had yet to update her 17 million Twitter followers on Friday, but since she is pushing her True Reflection fragrance it is a safe bet that she has forgiven and forgotten.
Andy Benson, a creative director at a Philadelphia advertising service, was less conciliatory. He said it was not the fact that Instagram needed to monetize the service that bothered him, but the way it had done so.
"Instagram was a social, creative tool," he said. "But now that Facebook is involved, it felt reckless to suggest that they could sell user-created content for their own financial gain."
Mr. Benson added: "The best advertising in the social media realm is a conversation -- it's not a monologue to the consumer. And that is what this felt like. 'Oh, we're going to let you use this tool, then take everything and sell it.' "
Mr. Cox had similar feelings. As the guardian for his 4- and 8-year-old nephews, he said he used the service to upload pictures of the boys and enjoyed the feedback of the "likes" he got through the service.
"But the idea that a year from now a Disney ad could pop up on my friend's Facebook page featuring a picture of my nephew feels like a bad TNT daytime movie," he said. "I want to be able to control what is out there."
The privacy brouhahas that Facebook has been involved in, the foundation noted, have involved attempts to adjust settings "in ways that meant your ability to keep some information private was no longer available." Facebook is operating under a consent decree with regulators.
Facebook and Instagram declined to say Friday how many people were quitting the service despite the policy reversal. They took a common approach of Internet companies after a scrap with their users: pretend nothing happened and move on. Instagram's blog featured a post about how it now was available in 25 languages. Mr. Zuckerberg has not posted on his Facebook page since Tuesday.
This article originally appeared in The New York Times.