Why can you use a photo of an unprotected 1913 painting in your public relations campaign?

The correct rationale is that the photo of the unprotected 1913 painting is in the public domain due to age. Works published in the United States before 1923 are typically considered to have entered the public domain, meaning they can be used freely without obtaining permission or paying a fee. Since the painting in question is from 1913, it falls into this category, allowing its use in a public relations campaign without concerns about copyright infringement.

While there may be other factors regarding copyright and authorship, the key element here is the age of the work, which clearly establishes its public domain status, thus enabling unrestricted use for promotional purposes.