I came across the picture which represents the piano keyboard with equally spaced black keys (as if two missing were added to ordinary keyboard).
The picture is a painting by Silvestro Lega, named Il canto di uno stornello (Wikipedia gives it as "Song of a Starling"). I do not know much about arts, so I read this artist is of XIX century (19th century), Italian.
I am quite intrigued to know - either this strange layout is simply a mistake of artist (who, perhaps, have made a sketch of a girl playing and later completed the picture "by memory") - or, given that other details of a picture are made scrupulously, it depicts some real variant of layout? Semi-mythical equal-tempered clavier?