Find a free service to host photos like ImageShack, etc. Do not use PhotoBucket as they charge a fee and no one will be able to see your images. Create an account there and upload your photos. Once you have done that, they will provide you with a URL to post your image into message boards. It will look like this,
(img)http://imageshack.com/yourimage.htm(/img)
Except you will use square brackets around the img instead of parenthesis. There is also a button at the top of the "post a reply" box that will insert that bit of code for you if you just want to copy and paste the URL here. If you prefer to do it that way just copy the URL from the address bar for the photo, come back here and hit "img" once you have started a new post and then hit CTRL+V to paste the url.
So this...
(img)http://image.fourwheeler.com/f/8306234+w660+h440+q80+re0+cr1/0610-4wd-01-z%2b2004-jeep-liberty-concept%2bfront-view.jpg(/img)
With square brackets, results in this...
Have fun!