I have some awful elisp code that glues together org mode, iimage.el and Deft to do something along these lines. All notes are stored as plain text with images in a sensible directory structure. I don't use git, everything just sits in a Dropbox folder. Emacs works well for me as the UI, but there's no reason a web-based UI couldn't be written. I could look into tidying it up over the Christmas break and publishing it if there's interest.