Abstract: Method and apparatus for inserting digital tracers in data that allow particular copies of the data to be traced to particular entities. Embodiments of a tracer mechanism may programmatically insert individualized tracers into data copies provided to third parties, for example via a Web service interface. A tracer may appear as normal data to the reader, and does not interfere with the typical use of the data copy. Tracers may serve as unique identifiers for particular data copies provided to particular Web service clients, allowing instances of the data copies to be associated with particular Web service clients. Embodiments may, for example, allow an enterprise to programmatically and systematically track copies of data distributed to third parties to help insure that the terms and conditions of licensing agreements are not violated. In one embodiment, the tracer mechanism may be implemented as a Web service.