As websites like Facebook and YouTube make it easier to share interesting videos and documents, more people are likely to get in legal trouble.

Most copyright laws don't distinguish between professional and amateur publishing, says Till Kreutzer of the German information portal irights.info.

"In principle, a private person faces the same sanctions. If you publish something online without the permission of the copyright holder, then it's forbidden and can have consequences."

Violations can cover anything from the upload of a wedding video featuring copyrighted music in the background to reposting a newspaper article on a blog.

But there are limits. Thus, just about every form of media is allowed to quote or cite the work of others. The problem is that there are no general rules on how many seconds or sentences one may reproduce before crossing a line.

"There are no absolute rules, just relative ones," explains Kreutzer. The main thing to remember is moderation. "If about 90% of a work consists of quotes, then that wouldn't be allowed."

German media lawyer Thorsten Feldmann says the true test is whether one used the old work to create something that could be considered a new copyrighted piece. "The copyright law only kicks in when a new work is created."

There's always the option of calling the owner and asking for permission, but Kreutzer sees that as a dead end. "If you want to use the piece of music for a video, you can find that there are up to seven copyright holders and 11 different kinds of law involved. It's an extremely complex process that's completely opaque for laymen."

Things are less complicated with photos, where one can usually just ask the photographer if he allows re-publication of his images.

Feldmann says the simplest option is to use pictures not protected by copyright. "There's a large selection of pictures that are under free license. Photos under this so-called creative commons license don't require a fee, though there are rules that must be followed."

"Usually it's enough to say the name of the copyright holder and to note the creative commons license," says Kreutzer. There are also often restrictions regarding altering the photo.

Also be aware of using photos depicting individuals. People need to approve the use of their image. It's even more complicated if minors are involved, as parental approval is also necessary.

Kreutzer says people are most likely to incur legal problems with the incorrect use of a photo or a piece of text. He sees as much lower the odds of someone pursuing a copyright case because some music was used in the background of a YouTube video.

But there's a first for everything. "You can never know," he says. And the risks are always greater on social networks or personalized websites, than with a relatively anonymous site like YouTube.

Another reason to be on the safe side: any legal case can likely result in significant expenses, starting with legal costs.