I was not thinking of this image--"Hatsuhana doing penance under the Tonosawa waterfall"--by Japanese ukiyo-e master Utagawa Kuniyoshi (歌川 国芳, January 1, 1797-April 14, 1862), but was pleased to find it just now. I intended to use one of the wonderful Hokusai waterfall images from the series Shokoku taki meguri ("Journey to the Waterfalls in All the Provinces"), circa 1832, but think this one a grand fit.
And here is a tiny biography of Lady Ise, along with translations of nine of her poems. They include the "hidden immortal"lines quoted in my poem.
Kisoji no oku Amida ga taki by Katsushika Hokusai (1760-1849)
("Amida Waterfall on the Kiso Road")