Please, click on “Reply” and you will see a form with the following instructions:

Upload your attachment.
After your file is uploaded you will see a link to this file. Please, copy it and paste it into your topic or reply.

So, please, upload your file and copy/paste a link to the file.
Or, if you know html, you can embed your image right into your reply.

<img src="link" />

Hope it helps!