Posting images here is mostly the same as other forum software. Here, there are three main methods. I'll list them in the order that I would recommend them be used.
1. Find an image host (eg: Imgur, Flickr, Photobucket), and upload your pictures. You can even use the Formiculture.com gallery to host your pictures if you want (more about that later).
2. Find the direct URL to the image file, which usually ends with an image file extension (eg: .jpg, .png, .gif). Some sites will specifically give you this URL, others you may have to obtain it yourself by pulling up the image in your browser and then copying the address.
3. Once you have the URL copied to your clipboard, while typing your post, you can either click the image icon near the center of the bottom toolbar of the graphical editor, and then paste that URL into the dialog box, or you can actually past it into an image tag like this:
1. Upload your image to the Formiculture.com gallery.
2. While typing your post, click the "My Media" button near the center of the top toolbar of the graphical editor, then find and select your image.
Third method (this if really just a backup method, and not recommended if not needed)
1. Simply paste the direct URL to the image into your post (for this method, only URL's ending in .jpg, .png, or .gif will work).