@anartist is right.
A URL is like a street address, or like a document path in your computer: it just tells you where a thing is. Everything that appears online has a URL; everything that doesn’t appear online, doesn’t.
If you want to find the URL of a picture on the internet, try clicking the picture. Often it links to the picture’s URL, and you can grab the URL right from your browser’s address bar. If that doesn’t work (if the picture isn’t a link, or if it links to something else), try what anartist said (right click > copy image location). If that doesn’t work, and if you know how to read markup, you can find the picture’s URL in the webpage’s source (right click > view page source).
If you want to provide a picture on your computer with a URL, you have to upload it somewhere.