You need to use a direct link to an image. The one you used isn't an image, it's a website.
A direct link to an image will usually end in .jpg, .webp, or .png

For example, the link for the below image ends in .png:
https://i.imgur.com/viVcTZ5.png

https://i.imgur.com/viVcTZ5.png

Wow, amazing. The IMG tag doesn't work for me now... Guess it's the newbie rank..