Why is the file uploaded to AWS S3 0B in size?

I am developing a webapplication with Flask as the backend and Nuxt JS as the frontend. I receive an image file from the frontend and can save it to my Flask directory structure locally. The file is ok and the images is being shown if I open it. Now i want to upload this image to AWS S3 instead of saving it to my disk. I use the boto3 SDK, here is my code:

Here is my save_picture method, that opens the image file and resizes it. I had the save method, but commented it out to avoid saving the file to disk as I want it only on S3.

def save_picture(object_id, form_picture, path):
    if form_picture is None:
        return None
    random_hex = token_hex(8)
    filename = form_picture.filename
    if '.' not in filename:
        return None
    extension = filename.rsplit('.', 1)[1].lower()
    if not allowed_file(extension, form_picture):
        return None
    picture_fn = f'{object_id}_{random_hex}.{extension}'
    picture_path = current_app.config['UPLOAD_FOLDER'] / path / picture_fn
    # resizing image and saving the small version
    output_size = (1280, 720)
    i = Image.open(form_picture)
    i.thumbnail(output_size)
    # i.save(picture_path)
    return picture_fn

image_name = save_picture(object_id=new_object.id, form_picture=file, path=f'{object_type}_images')

s3 = boto3.client(
        's3',
        aws_access_key_id=current_app.config['AWS_ACCESS_KEY'],
        aws_secret_access_key=current_app.config['AWS_SECRET_ACCESS_KEY']
)

print(file)    # this prints <FileStorage: 'Capture.JPG' ('image/jpeg')>, so the file is ok

try:
    s3.upload_fileobj(
        file,
        current_app.config['AWS_BUCKET_NAME'],
        image_name,
        ExtraArgs={
            'ContentType': file.content_type
        }
    )
    except Exception as e:
        print(e)
        return make_response({'msg': 'Something went wrong.'}, 500)

I can see the uploaded file in my S3, but it shows 0 B in size and if I download it, it says that it cannot be viewed.

I have tried different access policies in S3, as well as many tutorials online, nothing seems to help. Changing the version of S3 to v3 when creating the client breaks the whole system and the file is not being uploaded at all with an access error.

What could be the reason for this upload failure? I it the config of AWS or something else?
Thank you!

Thanks to @jarmod I tried to avoid the image processing and it worked. I am now resizing the image, saving it to disk, opening the saved image, not the initial file, and sending it to S3. I then delete the image on disk as I don't need it.