Seven in 10 children and young people in the UK have seen unsuitable images and videos online, according to a report.
It also found that many youngsters are sharing pictures they would not want their parents to see, with some sharing content with people they only know online.
The report, published to mark Safer Internet Day, gives an insight into young people's digital lives - revealing the extent that the internet is a part of daily life and the risks and pressures youngsters are under as a result.
The vast majority of eight to 17-year-olds questioned (84 per cent) told researchers they had shared a photo online in the last day, with around 17 per cent saying they had done so in the last hour.
Around 70 per cent of this age group said they had seen content which was not suitable for their age in the last year, while among 13 to 17-year-olds alone, almost half (45 per cent) said they had seen nude, or nearly nude, pictures of someone they knew being shared around their school or community.
In addition, just over one in five (22 per cent) of all those surveyed said that someone had posted an image or video in an attempt to bully them.
Three in 10 (30 per cent) admitted they had shared a photo they would not want their mother or father to see, while over a third (38 per cent) say they worry about losing control of a picture they had shared online.
And worryingly, nearly two-thirds (65 per cent) said they had shared a video or image with someone they only know online.
More than half (56 per cent) said they have shared pictures and films on a public social media profile, with nearly a quarter (23 per cent) saying they do not know how to control who can see their social media posts.
The findings also show that the central role of video and images in digital culture is putting pressure on children to look good online.
Young people take 12 "selfies" on average before posting one on a website, the report found - while 43 per cent said that they worry about how attractive they look when they share photos. This fear was more common among girls than boys.
The report did find that the internet is being used by young people for positive purposes - around two-thirds (67 per cent) said that in the last year they have posted an image or video for a positive reason, such as to support friends, share something interesting or to encourage others.
It is fair to say that in 2017 the internet is powered by images and videos
Will Gardner, a director of the UK Safer Internet Centre and chief executive of Childnet, said: "It is fair to say that in 2017 the internet is powered by images and videos."
"This can magnify the risks and pressures that young people face, while also offering fun new opportunities for self-expression and creativity."
"Today's findings remind us that with an ever-changing landscape, it is more important than ever to equip young people with the skills, knowledge, confidence and resilience to communicate using images and videos responsibly and positively."
The online poll of 1,500 eight to 17-year-olds was commissioned by the UK Safer Internet Centre and carried out by ResearchBods.