What is the best way to register when I have hundreds of published images from over the years, but I have no idea when they were taken?
If the images are photographs and if they were taken by the same photographer, you may be able to register them together as a Group Registration for Published Photographs. In order to take advantage of this option the applicant does not need to know the precise date that the images were taken. Instead, you may provide the year that the most recent photograph was taken. However, the photographs must be published in the same calendar year, and the applicant must provide publication information for each image in the group. If the application is submitted within three months after the photographs were published, the applicant may provide a range of publication dates (e.g., January 15 – April 15, 2016). In all other cases, the applicant should provide a precise date of publication for each image. The Office encourages the applicant to list the month, day, and year of publication for each photograph, but will accept a qualified statement of the publication date, such as “approximately,” “on or about,” or the like. Although the Office will accept a qualified statement, precise publication information may be necessary to enforce the rights in any particular work in court. For additional information, please see Compendium (Third) § 1116.6.
Rob Kasunic, Director of Registration Policy and Practices at the U.S. Copyright Office