This paper presents a technical overview of the capabilities and characteristics of technologies proposed for use as a means of providing copyright protection for digital information resources: a) Watermarks and fingerprints provide indication of ownership, and indication of the identity of a licensed user, respectively, by embedding security information in the digital object. This information may be perceptible (as in a backwash image), or, more conventionally, imperceptible. While this technology has some attraction for copyright owners, its security properties are limited. b) ‘Digital signature ’ is a popular term for one of the capabilities of public key cryptosystems (PKCS). As well as providing signature services (origin authentication), this technology supports content confidentiality and content integrity services. These services are reliable ('strong ' in the terminology of cryptography), but the technology is not designed for use in environments where data objects are subject to modification (e.g. by compression). Moreover, its deployment would be likely to incur a significant cost. The paper also considers further practical issues both for copyright owners and for the scholarly use of copyrighted material.