easy...just find your photo on the internet. then load it by itself by right clicking and hitting the option to load image in new window. Then you should see just the picture you want. Now go up and copy yhe URL out of the address box in your browser.
Now when you post, hit the IMG button up top. It will give you a pop up window asking you for a URL. Paste the URL you just copied into that window and hit OK. Now your image will be imbedded into your post.
Sometimes it gets picky and gives you a red X, even if there is a valid URL, as you see above.