If you click on reply and type your message, underneath, there should be save draft, preview and submit.
Under that, there should be two menu tabs - Options and Upload Attachment.
If you select the Upload attachment tab, you should see Browse...
Images have to be reduced in size before they can be used on the forum - around 500 pixels wide is a good size but it will accept up to 700.
There is more info here: http://poultrykeeperforum.com/viewtopic.php?f=27&t=77
Good luck!
Tim