How do I get an image to directly post in the message rather than the thumbnail you have to click on?

Put them up on the web somewhere. (Not here.) Then use the IMG tag and feed it the link.

But the thumbnail is nicer for people who don't have high bandwidth connections, because downloading the image is than optional.

They can start loading the page before they head off to their daily mammoth hunt.

I finished off all the mammoths in my neighborhood last week, so then I went and upgraded my connection to fibre optics, so the big images don't bother me any more (except that when they are too large to fit my screen, and I have to go to all the tedious work of pressing the "-" key in Opera to resize the image smaller).