Not sure I follow you saying it's not easy to inline images.
See: https://github.com/adam-p/markdown-here/wiki/Markdown-Cheats...
I still don't follow you; why is this an issue with markdown? Why do you see this as different than any other markup language (e.g, HTML)? Unless we're talking about something like Word documents, you'll have to host the image somewhere, which could be in your github repo. I still don't see why this is an issue.