The photos above are from 1923 and show wooden cabines (rentable changing rooms that doubled as bathrooms) on the beach in Copacabana. This is after sea baths (banhos de mar) became popular due to their purported medicinal benefits. While interesting in and of itself, it’s nearly impossible to find out more about them, like when they were installed, by whom, and when they were removed.
As I’ve been digging through the archives of the Revista da Semana lately (and probably for a long time to come), I found an article from March 10th, 1917 mentioning the cabine, and another from May 28th, 1921 titled O que falta ao Rio de Janeiro para ser a primeira cidade da America do Sul? that complains about there being zero changing rooms at Copacabana beach, but the author states that they can be found at any other beach of the time. I’ve also uncovered photos as late as the January 7th, 1928 edition of the same magazine showing two ladies posing in front of said cabins (see below).
A 2010 thesis, Um Jeito Copacabana de Ser, by Stela Kaz said the following about bath houses (which could be different from cabines) at the time:
“The bath houses, which opened near the Boqueirão and Santa Luiza beaches (downtown) so that ladies following their medical prescriptions for sea-baths could change their clothes, had walls made of wood which were full of holes, forcing the women to line them with sheets to discourage inconvenient gazes, even during the early morning hours…”