If you're using bash, you can simply run:
shopt -s globstar
for d in **/; do mkdir -p "$d"/Photo; done
globstar option makes
** match "all files and 0 or more directories and subdirectories". In other words, it matches everything recursively. Because of the
/ at the end,
**/ will match all directories and subdirectories (no files). Therefore, the
$d will iterate over all directories in the current directory and their subdirectories and the
Photos directory will be created in each of them.
-p flag of
no error if existing, make parent directories as needed
Here, I'm just using it to suppress error messages if the target directory already exists. Remove it if you want to see the errors.
Note that this will fail to create a
Photo subdirectory in a target directory that contains a file named Photo. You haven't specified what should be done in those cases though and all other answers posted so far also have this limitation.