Convert pyBarcode output to PIL Image file

I am trying to convert the output of pyBarcode to a PIL Image file without first saving an image. First off, pyBarcode generates an image file like such:

>>> import barcode
>>> from barcode.writer import ImageWriter
>>> ean = barcode.get_barcode('ean', '123456789102', writer=ImageWriter())
>>> filename = ean.save('ean13')
>>> filename
u'ean13.png'

As you can see above, I don't want the image to be actually saved on my filesystem because I want the output to be processed into a PIL Image. So I did some modifications:

i = StringIO()
ean = barcode.get_barcode('ean', '123456789102', writer=ImageWriter())
ean.write(i)

Now I have a StringIO file object and I want to PIL to "read" it and convert it to a PIL Image file. I wanted to use Image.new or Image.frombuffer but both these functions required me to enter a size...can't the size be determined from the barcode StringIO data? Image.open states this in their documentation:

You can use either a string (representing the filename) or a file object. In the latter case, the file object must implement read, seek and tell methods, and be opened in binary mode

Isn't a StringIO instance a file object as well? How do I open it as a binary file?

Image.open(i, 'rb')
>>> Image.open(i, 'rb')                                                                                                           
Traceback (most recent call last):                                                                                            
  File "<stdin>", line 1, in <module>                                                                                  
  File "/home/mark/.virtualenvs/barcode/local/lib/python2.7/site-packages/PIL/Image.py", line 1947, in open