People who use the popular photo and video sharing social network should prepare to deal with something they have never had to deal with before: advertising.

So far, Instagram has never had any advertising in the app experience. Don’t forget, the service has been completely free.

Instagram, however, is owned by Facebook. It was bought by Mark Zuckerberg and co. for $1 billion more than a year ago. And if you’re a public company with shares that trade on the stock exchange, you better show investors return on investment.

The ad announcement from Instagram came via anofficial blog post Thursday.

In it, Instagram says part of its plans involve building the social network “into a sustainable business.” Sustaining a business that doesn’t sell advertising or charge user fees is like trying to live without food or water.

The type of advertisements will come in the form of photos and videos “from brands you don’t follow,” Instagram says.

So, for example you could see an ad for sportswear from Nike. Or perhaps an Instagram photo from Ford. These are just hypothetical.

Instagram also says the ads will be consistent with the format of material we’re used to seeing, such as photos and videos shot with an eye for photography – and retro filters that bring out the best in the images.

Advertising in Instagram isn’t an easy subject to bring up. Users were outraged when a change to the social network’s terms of service opened the door to businesses using people’s photos as ads.