If you have an image hosted on a separate host like Imgur or Flicker, add the image source code (it ends in the photo name extension - .jpg, .png, and so on) and surround it with the IMG tags in brackets. "[img]" and "[/img]", except without the quotation marks. In your last attempt, it would be "[img]"https://i.imgur.com/mHHlD4s.jpg"[/img]", again, without the quotation marks.

Formerly TN Lone Wolf

"We are only as strong as we are united, as weak as we are divided." - J.K. Rowling