Click 'post reply'. To attach a file to a new post, click the button at the bottom of the post composition page, and locate the file that you want to attach from your local hard drive.
Only certain types of files may be attached: these are the valid file extensions for files to be attached to this board: gif jpg txt zip jpeg.
or
Surround the address of the image with the image tags: http://www... (without the space between the slash and img)
For further questions, take a look at the News & Questions forum and Help first to find the answer to your question. Most of the questions have already been answered there