Just a tip, you can preview a post / thread without actually posting, you just click on the 'Preview Post' button at the bottom of the reply window (You have to be in advanced mode)
Also, I'm assuming you want to have the image file maximised, and not as a small thumbnail like that?
You'll need to upload the image to an external hosting site (Or your own if you have one) something like Imgur is the best and most lightweight. Upload it there then grab the direct link, throw that in a pair of [img] tags and you're good to go!
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