So, I think I understand what the problem is. It looks like you are trying to create your own url by manually adding https to the name of the image you want to use.
If that is the case, then that method will not work. I tried the link for your picture of a penguin and it brought me to a website that specializes in family portraits.
If you want to use personal pictures that are only stored on your local device (mac, windows) you have to get them hosted online so the world can see that image.
There are a lot of sites that will charge for web hosting but I think the best option for images would be to use Github. You will need to create an account (free) and follow these instructions.
I hope that helps.