They need to be on the web already. You cannot upload pictures from your computer.

Then you use the image button from the toolbar and enter the web address of the image.

You can see the result if you quote me by using the quote button on my post.

Maybe your internet provider has given you the option to host a small homepage.

Or you can use a micro-blogging service like http://imgur.com/ or https://www.tumblr.com/