On some cases the same error happens when you are dealing with a Raw Image file such CR2. Example: http://www.rawsamples.ch/raws/canon/g10/RAW_CANON_G10.CR2

when you try to run:

byteImg = Image.open("RAW_CANON_G10.CR2")

You will get this error:

OSError: cannot identify image file 'RAW_CANON_G10.CR2'

So you need to convert the image using rawkit first, here is an example how to do it:

from io import BytesIO
from PIL import Image, ImageFile
import numpy
from rawkit import raw
def convert_cr2_to_jpg(raw_image):
    raw_image_process = raw.Raw(raw_image)
    buffered_image = numpy.array(raw_image_process.to_buffer())
    if raw_image_process.metadata.orientation == 0:
        jpg_image_height = raw_image_process.metadata.height
        jpg_image_width = raw_image_process.metadata.width
    else:
        jpg_image_height = raw_image_process.metadata.width
        jpg_image_width = raw_image_process.metadata.height
    jpg_image = Image.frombytes('RGB', (jpg_image_width, jpg_image_height), buffered_image)
    return jpg_image

byteImg = convert_cr2_to_jpg("RAW_CANON_G10.CR2")

Code credit if for mateusz-michalik on GitHub (https://github.com/mateusz-michalik/cr2-to-jpg/blob/master/cr2-to-jpg.py)

In case you write into the object first, make sure to reset the stream before reading:

>>> b = io.BytesIO()
>>> image = PIL.Image.open(path_to_image)
>>> image.save(b, format='PNG')
>>> b.seek(0)
>>> b.read()
b'\x89PNG\r\n\x1a\n\x00\x00\x00\rIHDR\x00\x00\x06\xcf\x00\x00\x03W\x08\x02\x00'

or directly get the data with getvalue

>>> b.getvalue()
b'\x89PNG\r\n\x1a\n\x00\x00\x00\rIHDR\x00\x00\x06\xcf\x00\x00\x03W\x08\x02\x00'