What did you do?

from PIL import Image
import numpy as np
a=Image.open('aa.jpg')
b1=np.array(a)
b2=np.array(a)

What did you expect to happen?

b1.shape == b2.shape == (H,W,3)

What actually happened?

Surprisingly, b1.shape == () and b2.shape == (H, W, 3).

b1:
array(<PIL.JpegImagePlugin.JpegImageFile image mode=RGB size=2000x2000 at 0x7FCD...48>, dtype=object)

I have a large RAM available (>50G).
This is consistently reproduced for a specific image file:
https://farm5.staticflickr.com/4360/36444958735_32c0410b64_o.jpg

What versions of Pillow and Python are you using?

5.1.0.dev0 && 4.3.0 (pip version)
Python 3.6.4