I just did this for the first time yesterday so I'm eager to answer. Find the image you want on the web, right-click it, and select "properties". Where it says "location", copy that info. When you come here to post your message, click on the "Img" button, and paste the location info. Then hit the "close tags" button in the menu, below the "Img" button. I posted an image below to see if my advice works...
Like a charm! It's that simple...