Instagram, the phone app that lets you take pictures, apply artsy filters and then share them, is huge. So huge that in 2012 Facebook bought it for $1 billion.

Then, late last year, Instagram did something massively stupid: it changed its terms of use, the document of rules for using the service. The new terms included this gem: “You agree that a business or other entity may pay us to display your username, likeness, photos … without any compensation to you.

The backlash was swift and vicious. Bloggers heaped disdain. People quit Instagram en masse. Lawyers filed a class-action suit.

The CEO of Instagram sheepishly apologized, reinstated the older agreement and explained: “Instagram has no intention of selling your photos, and we never did.” He had also remarked that “legal documents are easy to misinterpret.”

Yes, apparently they are. Instagram was hardly the first Web company to publish appallingly rapacious, tone-deaf terms of service, trigger a public revolt, and then backpedal and apologize.

In 2009 Facebook's new agreement stated that users gave the company perpetual license “to use, copy, publish … modify, edit, frame, translate, excerpt, adapt, create derivative works and distribute … any User Content you Post.”

After a ferocious public backlash, the company reverted back to its older terms (although it has again offered new ones). “It was never our intention to confuse people,” a spokesperson said. “Facebook does not, nor have we ever, claimed ownership over people's content.” Wait, what?

Google has lived through this cycle, too. When it introduced its online Google Drive storage, the terms-of-use document said (and Google's general policy still says) that if you put files onto the Google Drive, you give Google “a worldwide license to use, host, store, reproduce, modify … and distribute such content.

After ire from users, Google pointed to other language in its service agreement that says, “What belongs to you stays yours.”

What's going on here? Who owns your material?

“That sort of language is typical in any site with user-generated content,” says Los Angeles–based intellectual-property attorney Alan Friel, who writes these agreements all day long.

This “license to use, modify, distribute” talk is called facilitative rights. You're giving the company permission to process and display your stuff on their site. “Modify” means, say, “reformat for Facebook's template”; “perform” means “permitting playback of music or video you've posted”; “distribute” means “copying to multiple Facebook servers”; and so on.

What about the “derivative works” language? That's to protect media companies from lawsuits. “They're concerned that if they let users start posting stuff or submitting ideas, then they'll get sued when they create a TV show that may be similar,” Friel says.

In each terms-of-service drama, the public seems to think that the Web company is claiming ownership of content. Instead these agreements give the company a nonexclusive license to use your stuff, usually in innocent, or at least understandable, ways. But could a company take those rights literally? Could it “modify” your post beyond recognition? Could it license your Instagram photograph for use in an ad for something like the NRA?

Technically, yes. Yet it's unlikely. Consumers would revolt—and flee the service in droves. And by distributing a user's content to outside parties, a company such as Facebook or Instagram would cease to be protected legally if the content, say, was already copyrighted.

In the meantime, it's perfectly possible to write less inflammatory agreements. Compare Google's language with the terms for Microsoft, which offers a very similar SkyDrive service: “Your content remains your content, and you are responsible for it. We do not control, verify, pay for, or endorse the content that you and others make available on the services.” Boom. Done.

Surely these companies realize that normal people aren't lawyers. Why can't they say what they mean? Then again, we should be careful what we wish for. If these companies really said what they meant, they'd say, “We're here to exploit your creativity. If you don't like it, leave.”

Why your stuff on Facebook stays yours: