If you're posting a new topic it's pretty simple.
When posting "New Topic", on the lefthand bottom of page you will see "Attach Files" Click on that, a pop up window should show, click on "Photos" (lefthand side of pop up window) and click on the pic you would like to post, then click on "Choose" in pop up window, the pop up window should disappear. Once you have chosen your pic you then click "Attach This File". Once your picture uploads you then need make sure your curser in the post you are making is where you want it to be and then click on "Add to Post". Be sure your curser in your post is in the place you want it to be.
I believe when posting photos to an already active topic (such as this one) you need to click on the light blue box (More Reply Options) next to the black "Post" box at the bottom righthand side of these "Reply to this topic" boxes.