You can do it Val.
Right click on the photo that you want to insert in a post. Then click on "Copy Image URL"
Start your reply or new post. Click on the "Insert Image" icon, on the message toolbar.
Place your cursor between the square brackets
Right click and paste the URL between the square brackets
Go to Preview to see the post. Usually when the photos do not appear it's because the URL has not been pasted between the square brackets