To repost, you just go to the picture in the old thread, right click on the prior photo, select copy image location (or open the photo in its own page and copy the link at the top). Then on the new post, click on the insert image box (yellow with mountain range and stamp looking think) and paste the location in there.
for instance, here is the link from the top of the page:
http://www.shottalk.com/forum/images...head_right.gif
... and here is how will post with insert image
works the same from a thread, you just need the image link