There are multiple ways to post an image. These steps assume that you have already opened the page for your New Thread or New Reply, and have typed the body of your message that you want to appear. You should have the text input cursor at the place in the body of your post at which you want the image to appear.
Use your own hosting (e.g. Flickr, your personal web site, Image Shack)
If you are hosting your own pictures, either on your personal web site or on a commercial photo hosting solution such as Flickr or Photobucket, you will need to copy the file's URL to your clipboard first. This is done by selecting the URL of that image in a web browser such as Firefox or Internet Explorer, and then either choosing Edit, Copy or by right-clicking on the selected text, and selecting copy.
Once you have copied the URL, return to the window in which you are editing your New Thread or Reply, and type the characters [IMG=" then paste (Edit, Paste) the URL. Make sure to finish this with the characters "] .
Image Shack allows you to host an image and link to it without registering an account.
Attach your image to your post (Supporting Members only)
If you have upgraded your account to Supporting Member, then you may attach four images per post or reply. Scroll past the "Post Thread" and "Preview Post" buttons.
Click the button labeled Manage Attachments. (You may have to disable your pop-up blocker) The Manage Attachments window should now pop up. You may either (click Browse... to navigate to a file on your computer, press OK, and then press Upload) or (paste or type the URL of the file on the Internet that you are trying to attach, and press Upload). Repeat as needed for the other three images you are allowed to upload. After the file(s) has uploaded, scroll past the table of file extensions, and click Close this window.
Continue editing your new thread or reply, and when finished, submit your post.