Sadly I never purchased a monochrome monitor so I never had a collection of pictures. But I do remember seeing some great photos including 2 from Antic's 1986 art collection that included the great 640x200 Stoneage. Tom Hudson had graphic examples for every Atari resolution (including this very nice 640x400 picture I'm posting).
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There were some really good monochrome digitized pictures of Jack Tramiel with the ST on a few disks I got free with my STM I bought I remember, not pixelated like that one but looked much more like mono photographs. Think there was some butterflies too on the disk.