The system has been developed by Norwegian software firm FAST and will be rolled out fully in mid-April.
Copyright infringement is a big problem for online news publishers because most copy is very easy to 'copy and paste' from websites.
"We do see instances where our text stories, photos or video are used in part or whole and not credited or licensed correctly," said a spokesperson for Reuters.com.
"The Fast system has been designed to identify where a party goes beyond fair use of our stories - where they copy a full story and post it without licence or they derive a story from our content without sourcing it."
Reuters is not concerned about quotes included on weblogs or on other news sites that link to the original material. But the system will also allow the group to monitor which news stories are the most popular.
"This will help us make sure we are producing enough of the right material, keeping in touch with what the market wants."
Reuters has relied on manual content tracking until now, using its international network of 2,400 journalists to report on any copyright infringements.
The firm also uses video watermarking to mark video content, and plans to develop additional tools with FAST that will allow them to track unauthorised use of Reuters photographs.