Concerns about the impact of anti-circumvention legislation on public access and use of public domain materials is frequently addressed by arguing that the legislation only protects works that are subject to copyright. Since public domain materials fall outside that definition, works such as old public domain films that are enclosed with DRM could be lawfully circumvented. Those assurances notwithstanding, without the inclusion of a public domain circumvention right, circumventing DRM on works that combine public domain content with materials still subject to copyright could give rise to liability. In other words, pure public domain may be circumvented (provided you have the tools to circumvent), but once someone builds on a public domain work, they will benefit from the anti-circumvention provisions.
This is a particularly pronounced concern for historians, archivists, and film scholars since their ability to use public domain film or video may be limited by anti-circumvention legislation. For example, the distributor of a DRM'd DVD containing public domain films along with an additional commentary track would likely argue that there is sufficient originality such that the DVD is subject to copyright and that anti-circumvention provisions apply. While even supporters of the DMCA acknowledge that anti-circumvention legislation should not be used to privatize the public domain, they are loath to establish a full exception or circumvention right for public domain materials, arguing that all works contain some elements of the public domain and that a blanket exception could be used to cover virtually any circumvention.
A middle ground on this issue would include at least two provisions.