I had the very same problem when I started posting here a few months ago.
In order to post the image directly as you see others do you need to 1st upload the image to the web on a site like Flickr or Smugmug or similar web hosting sites.
Once you have your photo uploaded you can use the "insert image" option at the top of the box when you start a thread or reply to a thread. To do that, using Flickr as the example since that is one I use, open the photo in Flickr.
Click on "all sizes". Select a size that is around 800pix on one side, go down to the bottom of the picture and copy the URL. Then when you have the dialog box open on TPF select "insert image" and paste the url you copied there.
Hope that helps. It isn't as complicated as it sounds once you find the buttons.