cv2.imread always returns NoneType

First, make sure the path is valid, not containing any single backslashes. Check the other answers, e.g. https://stackoverflow.com/a/26954461/463796.

If the path is fixed but the image is still not loading, it might indeed be an OpenCV bug that is not resolved yet, as of 2013. cv2.imread is not working properly under Win32 for me either.

In the meantime, use LoadImage, which should work fine.

im = cv2.cv.LoadImage("D:/testdata/some.tif", CV_LOAD_IMAGE_COLOR)

In my case the problem was the spaces in the path. After I moved the images to a path with no spaces it worked.