Ah, well then, that changes things a bit. Apologies if you already know bits of this:
You're going to need somewhere to host it. (
http://imageshack.us/ is free and doesn't require an account; I suggest using them.)
Upload the pictures to them, and it will give you a bunch of text boxes with labels, including one labelled "Thumbnail for forums (1)". Copy the text in that text box into a new post on here, and you'll get a clickable thumbnail that leads to the full image.
Hope that makes sense. I'm not that good at explaining things.