It's still not working for me, but if I right click and select to view image I get a request to log in to Google. I never keep my browser logged in to Google. Once I did log in, it then still refuse to display the image, it gave me the no entry sign, so I assume the permissions are not set for it to be public. When I view again in the forum post now that my browser is logged in then I see the no entry sign within the forums too.
I'm afraid I can't help with Google Pictures, I have never used it. I personally use the public folder within Dropbox to share images on here. There are lots of other file sharing sites that allow forum linking out there.