We are getting a bit off topic here, but unless you are willing to paint an entire room a strange color like green and pay a ton of money for a fancy rig that gives you an exact 90 degree angle with two cameras, It's going to be difficult to do it by hand, or even with a tripod.
Best I have come up with for taking reference pictures is a tripod and a chair with the floor marked off with tape so that you can have a helper move the camera around you and take the pictures while you sit as absolutely still as possible. But even with this there will still be imperfections like lighting, position, you moved, etc. This will get it fairly close, but don't expect too much.
I've tried many times myself, taking a couple hundred reference pictures, and none of them are perfect. I had to manually edit almost every single one in GIMP. And that isn't counting the ones I've pulled off the internet that I had to edit, even blueprints, medical references, and technical drawings.
Even the pictures you are refering to that neodelito put up have minor issues: look at the lips, in the picture on the right the point #6 is lined up with the top of the lip, and #8 to the bottom of the lip, but in the front view they do not line up with thier respective parts, the picture is out of perspective slightly. Things like that are inevitable, eventually you just have say that it is good enough, not perfect, but usable.