Click on "manage attachments" to upload your photo. Once its uploaded it will be listed under "current attachments" with the file size, in the same window. Click on the file and it will open as a picture in a separate window. Copy the link in the address bar. Click on the little mountain picture on the toolbar above the box you type your replies in. When that window opens, paste the link you copied then click "okay". It will now appear in the dialogue box. When you click on "submit reply" the photo will appear in your post and it will not be a thumbnail. PM me if you need clearer instructions or have questions.
Pay no attention to the attached thumbnail. That was an oops. I was making sure I was giving you the correct insructions and forgot to delete the picture before I posted.