I've found the best way is to upload the photos elsewhere, then post here via the URL. I use imgur.com, but flickr or others work just as well. Once you upload, right click the image and select "copy image URL." The come over here and click the "insert image" icon. Select "from URL" and uncheck the box to rehost locally.

This method gives nice large in line images, not thumbnails. I've found that when you post directly here, you just get small thumbnails.