Github.com and Gitlab.com have after all put a lot of effort into their WYSIWYG editors, but they're not very useful for image uploads. That part should probab

Github.com and Gitlab.com have after all put a lot of effort into their WYSIWYG editors, but they're not very useful for image uploads. That part should probably be handled separately just to avoid slowing down the git repo with huge binary files. For example upload an image to S3, note the path, enter it into a markdown syntax image url. There are many ways to skin that cat, depending on the technical skill level of your client. They could even e-mail the images to a script, or message them to a bot on an IM service, that then returns the URL for them to use in Markdown.