The way I do it is upload a photo to google Photos and copy the URL to the photo box in the editor.

Paste the URL in the Markdown editor and wait until the image shows in the Preview section when you scroll down!

Screen Shot 2017-09-10 at 9.18.55 pm.png

If you click the link above it will show you what it should look like. It shows the link in the editor box and shows the photo in the preview box. Depending on your internet speed it will take some time for the photo to appear in the preview.

Thanks!