WELL, you can upload the image to PT itself if it meets the requirements... when you are making a post or reply, scroll down a bit until you see "manage attachments". Click the button and upload the image there.

But in order for an image to be shown on the internet, it first needs to be uploaded somewhere. You CAN show an image straight from your hard drive, but the link will be relative and only YOU would be able to see the image and no one else (unless that person just so happened to have the exact same image with the exact same name in the exact same spot on their computer as you do lol)