These are stereo conversions from regular flat paintings.
The original left eye image was changed to create the new image for your
right eye. They can be viewed as either cross-eyed, parallel, or anaglyphic.
My choice is the cross-eyed method. The easiest is the anaglyphic, with a pair of red/cyan glasses.
(Minimum screen size: 1024x768)
Cross Eye Version
1777 Johann Zoffany The Tribuna of the Uffizi
Oil on canvas, 123,5 x 154,9 cm Royal Collection, Windsor