A teenager's being sued over claims she was using Snapchat at the wheel as she crashed, leaving a man brain damaged.

Christal McGee's accused of using the app's speed filter, which lets users see how fast they're moving.

It's also claimed the 18-year-old kept on using the app after the crash, posting pictures of her injuries and saying she was "lucky to be alive".

Lawyers for Wentworth Maynard, who was a passenger in the other vehicle, say he now needs constant care from family.

In a statement, Wentworth's wife Karen says he's so tired he falls asleep in his wheelchair during the day.

"We used to sit on the sofa and watch TV in the evening, and Wentworth would hug me," Karen Maynard claims in court papers. "Now, he can't do that any more."

Christal McGee and her passengers were treated for minor injuries.

The court case, filed by the couple in the US state of Georgia, also targets Snapchat.

They argue the firm should have known the filter could be dangerous and that it would encourage distracted driving and speeding.

"This is a product liability case because Snapchat put something very dangerous in the marketplace without any warnings or safeguards," their lawyer argues.

"McGee wanted to post an image of herself going fast," they say.

Lawyers claim Christal McGee had said she was "just trying to get the car to 100 miles per hour to post it on Snapchat".

Snapchat disputes the claims, saying the app discourages people from using the filter at the wheel.

"No snap is more important than someone's safety," it says.

"We actively discourage our community from using the speed filter while driving, including by displaying a 'Do not Snap and Drive' warning message in the app itself."

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