This site has a different set of pictures of the oxherding pictures and the same translations as posted before by Paul Reps. The very first page explains the significance of the circle. The site has this information but not who did the pictures or scrolls that they are from: The Zenga introduction is by Matthew J. Dorn; the poems themselves are by Kakuan, a 12th century Chinese master, translated by Nyogen Senzaki and Paul Reps, as presented in Zen Flesh, Zen Bones; the commentaries are from Zen, by Martine Batchelor.