But we do have such images: https://i.pinimg.com/originals/b0/53/42/b053425982ecb933ca4cb9efb9dd5177.jpg https://i.pinimg.com/originals/b0/53/42/b053425982ecb9

But we do have such images: https://i.pinimg.com/originals/b0/53/42/b053425982ecb933ca4cb9efb9dd5177.jpg https://i.pinimg.com/originals/b0/53/42/b053425982ecb933ca4c... https://www.easy-drawing-lessons.com/images/xpainter-using-a-grid.jpg.pagespeed.ic.2ziN2OUHu1.jpg https://www.easy-drawing-lessons.com/images/xpainter-using-a... And their existence is part of critic's arguments against the Hockney thesis: many tools have been used in various ways at various times, and there's been little or no shame in acknowledging and documenting it. To accept Hockney-Falco, you'd have to accept the opposite: that such devices were widespread amongst artists but kept secret or never mentioned. I think Occam's razor suggests that if such devices were commonly used, it wouldn't be so hard to find evidence of it.