You can't upload images to Agora (aside from your avatar), to post images in threads you need to upload the image to another site such as imgur and then place the URL to the image file inside [img] [/img] tags.
Agora development hiatus
I'm pausing development on Agora for another month or so. The next major goals on my list was adding multiple boards, and batching queries together to make loading topics and the board indexes much more efficient. Since I am doing an independent-study-ish course focusing on SQL this coming semester, I want to save that work for when it'll count for the class credits. Sorry to those of you who were waiting for more progress on this system!