Click on "editor" on the top right of the text entry field and it will prompt you with an option across the top to link an image. The image will have to be hosted on a site such as imgur.com - Make sure to link directly to the image (the file extension (.jpg, .gif, .png) will be at the end of the link). I've noticed in the preview box beneath the editor that images aren't showing up, but they are working within the actual post. Hope this is helpful!