Defendants in personal injury cases often go to great lengths to prove the plaintiff's claims are either exaggerated or invalid. At one time, that meant hiring a private investigator to follow the plaintiff around and trying to capture evidence that contradicts claims made in the lawsuit.

Today, finding evidence to support the defendant's case is as easy as following the plaintiff on social media.

All across Canada – and in other parts of the world – social media posts are being used as evidence in personal injury.

In March, the British Columbia Supreme Court rejected one woman's claim for hundreds of thousands of dollars in damages after photos on Facebook contradicted her claims.

The woman said two car accidents left her without friends, depressed and unable to leave her home. But 194 pages from Facebook and hours of surveillance video proved otherwise. The woman was seen out with friends and river tubing – activities that contradicted her claim.

""The goal of a tort claim is to compensate you for pain and suffering damages, such as psychological injury, loss of income due to any missed work as a result of your injuries, out of pocket expenses, and anything else your accident benefit claim doesn’t cover,"" says MG Law, a firm that specializes in personal injury law.

But psychological injuries have always been notoriously difficult to prove, but with social media, it becomes even more difficult to support a claim. Many experts question whether posts on Facebook and Twitter can really be used as evidence in these types of scenarios, as people tend to only post things they want other people to see. Typically, that means posting images and updates that paint them in a happy, sunny light.

The Vanderbilt Journal of Entertainment and Technology Law published an article in 2012 that explained the dangers of using ""happy"" Facebook pictures to refute claims. The author cautioned that presenting these images may mislead juries and judges about the plaintiff's true emotional state.

People often use Facebook, Twitter and other social media platforms to keep up appearances.

Gaining access to private social media accounts can also prove to be challenging. A judge must be convinced that the information is relevant before handing over access. Even when access is granted, judges may not give the evidence a whole lot of weight.

In 2010, the Superior Court of Ontario ruled in one case that an injury plaintiff cannot expect privacy in regard to Facebook accounts, as the information is often shared with large groups of people. That ruling lowers the expectation of plaintiffs being able to keep their social media accounts private.

In that particular case, the plaintiff claimed his injuries prevented him from sitting in front of a computer for more than 15 minutes. The court ordered him to produce his private and public Facebook information.

Still, as social media continues to dominate the lives of most Canadians, posts will be used as evidence to refute or support a claim. Many Canadian lawyers are now telling new clients to be prepared to disclose employment, medical and social media records.

Whether or not those posts hold weight as evidence will depend on the case and the judge. In the above-mentioned case, the judge felt there was enough evidence to contradict the plaintiff's claim that she was a ""homebody"" and depressed.

In other cases, however, judges have argued that Facebook posts are merely a snapshot of a person's life and not a true picture of that person's mental health.

Many experts recommend being cautious about the content of social media posts, while others say to avoid it altogether while the case is pending.