An even simpler (and quicker way) to post an image that is already in your 'images' section is to write a post as normal and when you are ready to insert an image if you look at the taskbar just above your post you'll see a square, yellow icon (sort of looks like two mountains with a sun over them). Clicking on this will link directly to your 'images' page, and from there just 'insert' the image you want.
Although this only works with Internet Explorer. In other browsers, you can use html to insert a picture somewhere. I don't know the html for that offhand since I rarely need to use it, but it's not hard to find instructions online.