I recently discovered that draw.io will export an "Editable PNG" that embeds the entire diagram into the zTxt section of the PNG and I'm still geeking out about it. The diagram isn't immediately readable though... It has been Base64 encoded and deflated so that it doesn't take up as much space on the image. You can use TweakPNG to view the zTxt section in the PNG and this draw.io convert tool.