Perhaps you mean stereographs, if so they work because you get a separate photo for each eye up close, with a seperator, with or without lenses. https://en.wik

Perhaps you mean stereographs, if so they work because you get a separate photo for each eye up close, with a seperator, with or without lenses. https://en.wikipedia.org/wiki/Stereoscopy https://en.wikipedia.org/wiki/Stereoscopy https://www.vam.ac.uk/blog/caring-for-our-collections/stereographs https://www.vam.ac.uk/blog/caring-for-our-collections/stereo... https://news.library.mcgill.ca/double-takes-a-brief-history-of-stereographs/ https://news.library.mcgill.ca/double-takes-a-brief-history-... https://restoreoldphotosnow.com/what-are-stereographs/ https://restoreoldphotosnow.com/what-are-stereographs/ https://guides.library.oregonstate.edu/earlyphotoformats/stereographs https://guides.library.oregonstate.edu/earlyphotoformats/ste... Another method would be anaglyph, red-cyan or amber-blue dubois requiring similarly coloured glasses. https://adcnj3d.wordpress.com/the-science-of-anaglyph-3d/ https://adcnj3d.wordpress.com/the-science-of-anaglyph-3d/