How to Get a URL for Your Image
If you want to use an image that's already online, simply navigate to it > right click > Open Image in New Tab. When it comes up in a new tab simply copy the URL in the address bar.
If your image is not yet on the web you will need to host it somewhere. There are many ways to do this. You can put it on your website or blog, for example. If you do not have access to either of those databases, the simple thing to do is to use a public image hosting service like Imgur or Google Photos.
If you choose to go the Imgur route, just go to the website and click 'New Post'
Upload the file from your computer and copy the newly made URL on the right. No need to sign up or share to the community.
If you have a gmail account it will be just as easy for you to use Google photos. Once you sign in, you will upload your image and then right click on it > Open Image in New Tab. When it comes up in a new tab, copy the URL in the address bar.
Be advised that hosting your image online will make it searchable on Google.