How to get image size (bytes) using PIL

If you already have the image on the filesystem:

import os
os.path.getsize('path_to_file.jpg')`

If, however, you want to get the saved size of an image that is in memory and has not been saved to the filesystem:

from io import BytesIO
img_file = BytesIO()
# quality='keep' is a Pillow setting that maintains the quantization of the image.
# Not having the same quantization can result in different sizes between the in-
# memory image and the file size on disk.
image.save(img_file, 'png', quality='keep')
image_file_size = img_file.tell()

NOTE: if you use a different quality setting for each method you can end up with a smaller size in one or the other.

This method will avoid multiple reads of the image data as with StringIO. Note, however, that it will use more RAM. Everything is a tradeoff. :-)

Edit: I just saw this comment from the OP:

finally, the problem is from the beginnig, if someone will upload a picture that have 1 giga (forged one) he'll kill the server before PIL will do its stuff, so i must block the request before it finishs!

This is a very different question, and is probably best accomplished at the web server. For nginx, you can add this to your configuration:

http {
    #...
        client_max_body_size 100m; # or whatever size you want as your limit
    #...
}

Try:

import os
print os.stat('somefile.ext').st_size

To find the Size(In bytes) of an image using Pillow Library, please use the below code. It will working fine.

from PIL import Image
image_file = Image.open(filename)
print("File Size In Bytes:- "+str(len(image_file.fp.read()))

Make sure that you have pillow library installed:-

pip install pillow

I think this is the true measure and the fastest one of the size of the image in bytes in memory:

print("img size in memory in bytes: ", sys.getsizeof(img.tobytes()))

Then, the size of the file on disk depends on the format of the file:

from io import BytesIO
img_file = BytesIO()
img.save(img_file, 'png')
img_file_size_png = img_file.tell()
img_file = BytesIO()
img.save(img_file, 'jpeg')
img_file_size_jpeg = img_file.tell()
print("img_file_size png: ", img_file_size_png)
print("img_file_size jpeg: ", img_file_size_jpeg)

Possible output for 32 x 32 x 3 images from CIFAR10 dataset:

img size in memory in bytes:  3105    
img_file_size png:  2488
img_file_size jpeg:  983