if os.path.isdir(args.img_path):

This line of code checks if the argument passed to the script as "img_path" is a valid directory path.

The function "os.path.isdir()" returns a boolean value indicating whether the argument is a directory or not. If it is a directory, the function returns True, and if it is not a directory, the function returns False.

If the argument is a directory, the script can proceed with further operations that require accessing the files within the directory. If the argument is not a directory, the script may terminate or prompt the user to provide a valid directory path.