Out of curiosity, what would such a model be used for? I worry that as ML is becoming more popular and powerful, people are jumping to use it on problems from which the answer cannot possibly be identified accurately from the inputs alone. This model's predictions would entirely based on historical trends of what images looked like, rather than something objective like carbon dating.

I am not discouraging someone from building such a model, but it would be really helpful to know the context for which such a model is being developed. If it's just a hobby investigation, it would be cool to see how "predictable" dates are from images. I could even see it being used in forensics to provide a "first guess" as to when an image occurred, and helping with triaging of evidence. However, things become deeply problematic if the result from the image is fed to people as "ground truth" simply because the model was found to be accurate on a validation dataset. I certainly wouldn't want this model to be used to determine whether a suspect is innocent / guilty, or to be used naively by museums to date photographs.