I think only MOD's can do attatchments.
What you need to do is:
1 - Upload your photo to a secondary site (Ofoto, Webshots, Photobucket, Snapfish, Imagestation, etc.)
2 - Right click on the photo and highlight the properties and copy them.
3 - Return to this site, reply to thread, and click on the photo box above.
4 - Press "Control+V" at the same time to paste the code.
5 - Click Okay. Click submit reply.