Draw.io does this. When you export a diagram as a PNG. There is an option to embed the source file in the png. If you subsequently open one of those PNGs in Dra

Draw.io does this. When you export a diagram as a PNG. There is an option to embed the source file in the png. If you subsequently open one of those PNGs in Draw.io you can carry on editing it. I find it really handy.