with open(photo_file, 'rb') as image:
    image_content = base64.b64encode(image.read())
service_request = service.images().annotate(body={'requests': [{'image': {
    'content': image_content}, 'features': [{'type': 'LABEL_DETECTION',
    'maxResults': 1}]}]})
response = service_request.execute()
Как вызвать API Google Vision с изображением, хранящимся в Google Cloud Storage?