Or to get all technical and webby about it.... use tags! Upload the image to a host somewhere like Photobucket or Picassa. Find the url for the image - looks like a web address ending in a pic file format like .jpg or .gif. Copy the url and paste it into your post. At the beginning of it, start with as the beginning of the image - called a tag. At the end, write the same thing but put a "/" before "img". The program will recognize the url as an image instead of a link and you'll be all set!
By the by, can't explain the end tag by just writing it as [/whatever] because it'll trick the programming into thinking that all the text I wrote is an image url. Go figure! lol