Q: I am looking to publish a family history and genealogy using an aerial photo of the family farm as the front cover.

A: This is a tricky situation. Copyright infringement is strict liability, so your intent not to infringe doesn't save you from a possible claim of infringement. Whether the image is actually subject to a copyright claim is unclear, since it was created before 1978. If it was published or registered before 1978, then any copyright is most likely expired. If it was not published or registered before 1978, then a copyright may still be alive and well. If you really need to know, hire an IP lawyer who can give you more specific guidance.

Now, practically what you could do (even though it still would not save you from a claim), would be to explicitly note in the publication that you pursued diligent efforts to locate the copyright claimant/creator but were unable to do so, and invite anyone claiming rights to the image to contact the publisher to arrange for payment of a reasonable royalty. That's pretty risky, since you're essentially admitting copyright infringement if there is a valid/unexpired copyright, but would be helpful to show that your infringement was not in bad faith (and thus limit your possible liability). The obvious alternative is not to use the image! Maybe take a new photo? That way you'll have a clearer right to use it. BUT, there may be other considerations in whatever photo you do use, such as hidden trademark issues (unique identifying features in the image that function as a mark that is still being used in commerce). Good luck!