Under "Quick Reply" make sure you are on Advanced, if not select Go Advanced. There are a lot of buttons now at the top of the text box. Select the down arrow next to the paper clip. A new window opens up. Select the top Browse button. Then navigate to where the picture is and select it. This should take you back to the Browse page. Select Upload and wait until it finishes (sometimes it takes a while). Now, leave the Browse page alone and go back to the Reply to Thread page and select Submit Reply. The image should appear on the post. If a picture won't upload it is normally because it is too large and needs to be reduced in size. The size limits are listed on the Browse page.