They were kept in the photo because they were standing still.

Boulevard du Temple

Louis Daguerre，1838

The earliest known photograph is “View from The Window at Le Gras" taken by Joseph Nicéphore Nièpce in 1826 using the "heliograph" technique, which was the first permanently preserved photo in the history of photography. But the "heliograph" technique requires about eight hours of exposure time, which made it only suitable for still life shooting.

In 1838, French chemist Louis Daguerre invented a practical photography technique called Silverplate photography, which reduced the exposure time to about seven minutes. Louis Daguerre took the photo "Boulevard du Temple", which is widely considered the first photograph to contain a human figure. The photograph shows a busy street, but due to its still rather long exposure time, only the bootblack and his customer at the corner of the street, who were standing still, were able to be clearly captured.

Daguerre publicly announced his invention to the French Academy of Sciences in January 1839. On August 19, 1839, the French government announced that this invention patent was to be shared with the world free of charge.