Ron Turner Witches, 1959, and Pedigree Books
The “wonderfully lurid cover” of this book masks the serious nature of the text, as the Lilly Library notes (here). So does the advertising copy: “Weird Rites of the Middle Ages and the Black Mass.” The artists is—apparently—Ron Turner (1922–98), but no sources are cited for this on Wikipedia.
As for the date, almost everyone gives the original copyright date, 1957, which is actually the publication date for the first edition of the book (London: Chatto & Windus, 1957). (Which has a very boring cover by Paul Hogarth.) But this book clearly came out after the Pedigree edition of Jules Michelet, Satanism and Witchcraft: A Study in Medieval Superstition—which was issued in May 1959—because Michelet’s Satanism and Witchcraft is advertised on the back of this edition of Hole’s Mirror of Witchcraft (below).
The Pedigree reprint of Gerald Gardner Witchcraft Today was first published in 1960 and it is not mentioned on Hole’s Mirror of Witchcraft, so perhaps the latter dates from late 1959 (between Michelet’s Satanism and Witchcraft of May 1959 and Gardner’s Witchcraft Today of 1960).
It certainly must be at least a few years later than 1957. As it states on the rear cover: “This is an original PEDIGREE BOOKS reprint, Complete and Unabridged, of a book hitherto available only in full cloth-bound form and priced at 21s. net.” As you can see, this Pedigree Books paperback is only 3s 6d. I can’t see the publishers licensing a reprint until their ugly hardcover had sold out.
Looking around, I could not find any copies of this edition in any library on Copac or Worldcat (each of which is a kind-of Google for books held in major libraries around the world) and only three copies for sale via AddAll and eBay: none provide any useful details about the artwork, the date of publication etc.
I must say I was really surprised that there wasn’t a list of Pedigree Books publications online somewhere. They all have such outrageous covers that someone must be collecting them! I only have the three I mentioned—the cover to Mirror of Witchcraft is the only one with sexy witches—but I have seen three others. The lists is:
 Gerald B. Gardner, Witchcraft Today (London: Rider, 1954; repr. Pedigree Books, 1960). ¶ Cover art by S. R. Boldero. For more on S. R. Boldero, see here.
 Christine Hole, Mirror of Witchcraft (London: Chatto & Windus, 1957; repr. London: Pedigree Books, n.d. [1959?]). ¶ Cover art by Ron Turner.
 Donald McCormick, The Hellfire Club (London: Jarrold, 1958; repr. Pedigree, no date). ¶ Details here.
 Jules Michelet, Satanism and Witchcraft: A Study in Medieval Superstition, trans. A. R. Allinson (Paris: Carrington, 1904; repr. London: Pedigree Books, May 1959). ¶ Reprinted July 1960. Cover art by S. R. Boldero.
 H. T. F. Rhodes, The Satanic Mass (London: Rider, 1954; repr. Pedigree Books, 1957). ¶ Cover art by Ron Turner.
 Gerald Verner, ed., Prince of Darkness (London: Rider, 1946; repr. Pedigree Books, 1960). ¶ Cover art by S. R. Boldero