If you want to load a picture directly to the site there are a couple ways.
You can create a photo album in your profile, upload the picture to that and then link it into the thread.
Or, as I did here...
1. Click the "Go Advanced" button below the reply window.
2. Click the paperclip symbol in the top row of buttons.
3. "Choose" the file then "Upload" it.
The picture is now attached to the post as a thumbnail. Now, if you want, you can embed the picture into the post as well, as I did below.
1. Click the "Preview Post" button
2. Click on your uploaded image thumbnail to open it in a new window
3. Copy the URL from the address bar
4. Click the back arrow in your browser
4. Click the picture button
5. Paste the copied URL of your picture into the field in the picture URL dialog box.