The photograph is from Celtic Myth and Legend (1905) by Charles Squire (fl. 1905). See also Early Celtic Scholarship and the Romantic Celt: Charles Squire by Juliette Wood, Cardiff University. Newgrange predates Irish Celts and was built by the Neolithic Irish---in fact, there's a Neolithic Irish aos si (person of the mounds: an Irish fair folk or elf: see also aos si pronunciation) standing in the entrance beyond the megalith with the triskelions.