In order to reduce the size of images to be used in a website, I reduced the quality to 80-85%. This decreases the image size quite a bit, up to an extent.
To reduce
You don't even need to do the extra steps @user2141737 suggested. Just opening it up with PIL and saving it again seems to do the trick just fine:
from PIL import Image image = Image.open('path/to/image') image.save('new/path/' + file_name)