The discovery of an image of Rehtaeh Parsons, the Nova Scotia teen who died in April, in an online dating ad on Facebook has outraged her parents and put the social media site on the defensive.

It's yet more proof that it is almost impossible to control where images uploaded to the internet ultimately end up.

"This is a textbook example of the fact that everything we put online we immediately give up or give over to whoever wants to use it," says Sidneyeve Matrix, a media professor at Queen's University in Kingston, Ont.

Parsons is the Nova Scotia teen who died in April at 17 after a suicide attempt. Her parents said she was sexually assaulted when she was 15, and then bullied about it for more than a year.

The ad in question, for a company called ionechat.com, carried the title "Find Love in Canada!" and featured the description "Meet Canadian girls and women for friendship, dating or relationships."

The ad was spotted by a Toronto man while he was checking his Facebook account.

In a written statement, a Facebook spokesperson called it "a gross violation of our ad policies." Facebook has since deleted the ad as well as ionechat.com's account.

Image 'scraped' from another site

On Wednesday, Anh Dung, the administrator of ionechat.com, admitted that the images of Parsons had been gathered randomly from Google by a so-called image scraper. This refers to an automated computer script that downloads or grabs online images based on given parameters.

Companies scrape images all the time, says Matthew Johnson, director of education for the non-profit organization MediaSmarts, but there have been some high-profile examples that illustrate how problematic it can be.

In 2009, a Missouri family was travelling in the Czech Republic when they saw their faces on the side of a bus in an ad for a local grocery store.

The mother, Danielle Smith, said the original photo, which Smith subsequently shared on social media, had been taken by a family friend. The owner of the grocery store said he had found it on the internet, and assumed it was computer-generated and free to use.

Terms of use 'difficult to read'

Johnson says the issue of online image-sharing is complicated by the fact that the terms of use on most social media sites continue to be incomprehensible to many people.

"While most of the major services that feature image-hosting have tinkered with their privacy settings, and in many cases made those more powerful, the privacy policies and terms of use have in general remained very difficult to read," he says.

"They're written by the lawyers, and no translation is provided."

For example, Facebook's data use policy states that regardless of what you upload, "you always own all of your information." But the company still has full use of that content and can pass it on to third parties, technology writer Carmi Levy told CBC News.

"The company makes it very clear that you own it, but they also have the right to use these pictures, technology, video, materials and whatever you post in whatever capacity they wish in perpetuity," Levy said.

"So basically you're signing it over to them for them to use as they wish, as soon as you upload it."

Different countries, different laws

Johnson says the issue is further muddied by the fact that different countries have different laws governing the use of photos posted online.

Businesses in countries that are not part of international legal agreements are more likely to cherry-pick images off the internet without paying for them, he says.

If the business "is based in Croatia or Nigeria, or one of these places, it can be a challenge [to stop them from using the image]. And certainly there are cases where businesses opt to have their servers hosted in those countries for those reasons."

Queen's University's Matrix says the unfortunate use of Parsons' image in an ad could be a "teachable moment" for parents trying to instruct their children to be vigilant about uploading photos to the internet.

"We are in a new day where people think that if they find something on the web it's free to use, and that's not necessarily the case," she says. "In this case, we're seeing the hurt that that can cause."