Ask Ubuntu has a built-in image uploader, but you can only use it if you have [at least 10 reputation](https://askubuntu.com/help/privileges/new-user) to prevent [abuse](https://meta.stackoverflow.com/q/268469/4751173).

The alternative is to upload them somewhere else (e.g. the [main imgur site](https://imgur.com/)), post a *link* to the image, and hope another user will convert them to proper inlined images.