input: Write a python function to scrape photos and captions from a given website.
  assert scrape_photos_and_captions('https://example.com/webpage') == [('https://example.com/photo1.jpg', 'Caption 1'), ('https://example.com/photo2.jpg', 'Caption 2'), ('https://example.com/photo3.jpg', 'No caption')]
  assert scrape_photos_and_captions('https://example.com/empty-page') == []
output: def scrape_photos_and_captions(url):
      import requests
      from bs4 import BeautifulSoup
  
      response = requests.get(url)
      soup = BeautifulSoup(response.content, 'html.parser')
  
      photos_and_captions = []
      images = soup.find_all('img')
  
      for img in images:
          photo_url = img.get('src')
          caption = img.get('alt', 'No caption')
          photos_and_captions.append((photo_url, caption))
  
      return photos_and_captions