If this isn't working for you, I would try a different web browser, as it sounds like something is blocking your web browser from inserting the [ img ] tag properly. You can also likely just use the [ img ] tag directly into the browser if your browser doesn't support the use of the insert image icon.

Also, if you're trying to post images from Facebook, that may often not work due to the permissions of the original image (e.g., you may be able to see the image fine, but it may not be set to be seen by the general public or non-logged in Facebook users).

You need to copy the file to your computer and upload it here, and then link to that uploaded image.