EpicEditor is an embeddable JavaScript Markdown editor with split fullscreen editing, live previewing, automatic draft saving, offline support, and more. For developers, it offers a robust API, can be easily themed, and allows you to swap out the bundled Markdown parser with anything you throw at it.
Add some multipart form to receive drag and drop file uploads. Then we configure some endpoint that will save the image and return the url.
Similar to the GitHub editor.