Click "Go Advanced" in the Quick Reply box, or click "Post Reply" at the bottom of the other posts.
Click the attachment icon. (It looks like a paperclip)
A small window will pop up.
Click on "Upload".
When you have located the image, click on it to upload.
Close the Popup box.
Click on the paperclip icon again and select the image you want to insert by clicking on the file name.
This will insert the image to your post. If you skip this step of inserting the image where you want to display it, the image will show as an attached thumbnails at the bottom of your post.
Hope this helps.