I'm very beginner at org-mode and learning and having fun with it these
days.

Now, I'm embedding an image, but I'd like to resize it.

Googling shows me like this:

#+attr_org: :width 40%
[[./test.png]]

However, that is not working to me at all.

I'm using

GNU Emacs 25.1.90.1 (x86_64-apple-darwin13.4.0, NS appkit-1265.21 Version
10.9.5 (Build 13F1911)) of 2016-11-28

Org-mode version 8.2.10 (release_8.2.10 @
/Applications/Emacs.app/Contents/Resources/lisp/org/)

Anyone can help on this, please?

C-c C-x C-v shows only original image size. What should I need to check
more?