"Book of Supreme Signs": It is cited in the book "Chag HaPesach (Passover)" by Rabbi Yaakov Kitzingen (Krakow, 5377). In the list of books by Rabbi Moshe David Oppenheim, there's a mention of the book "Otot" (Signs) that God showed to Ezra the Cohen. In the book "Likkutei Shas" by the Arizal, there's a reference to the "Book of Letters" which is the reasoning behind the images of letters (Rav Pe'alim 38). It seems that this is the "Book of the Image", see there.