Just create a new post (New Post button (top right corner)), and click the "Add Image" button next to the "spellchecker" button.
Then just follow the onscreen instructions:
you can either,
- upload it from your computer, or memory card, or camera connected by USB.
- Or if you have already loaded them to facebook, flikr, or another image hosting site, just right click the photo and copy the image url and paste it into the url box (try right clicking the kittens below to see what I mean).
Sam