I have tried both the sites mentioned but when I try to insert the link it doesn't work. in fact if I try to insert any link it tells me that I am not allowed to post links on this site.
I would pull the hair from my head if I had any .
How the heck Bigfoot Mike managed to get a picture up is way beyond me .
This is the URL of the link in your post:
https://postimg.cc/gallery/16udos0jg/
This isn't an image because an image file would include (end with) a filename - e.g. photo.jpg
In other words, the URL would look like this:
https://postimg.cc/gallery/16udos0jg/photo.jpg
If you're copying and pasting a link to an image, you need to ensure that the entire link is included.