If you have an image on your own device (e.g., gallery on your phone), there are free images hosting sites like Imgur, and Postimages.org

For the markdown here you will need the link directly to your image, not a link to a web page that displays your image.

For example, with Imgur, there are two links:

So to display that in a comments you would use:

My preference for image hosting is PostImages.org,

![My image](https://i.postimg.cc/pPd0Bfy5/SPtEPn5.png)