Earliest photo of famous person?

Maria Edgeworth is still a well known writer, in Ireland at least. I don’t know how widely her name would be recognised elsewhere.

From your link, it appears Pierre Stephen Du Ponceau (1760–1844) was the earliest born person in a photograph. A linguist who correctly refuted European myths about Chinese writing, he was famous enough to have a Wikipedia article.

Conrad Heyer was born either in 1749 or 1753. In the early 1850s a few Revolutionary war vets were photographed. Not famous though.