Resolved the issue
The Image.Source property expects to get an ImageSource object.
But your Data.ImageSource property is returning a string.
So you need to convert that string into an ImageSource by using a Converter.
The BeatPaths sample includes such an example that you can adapt for your own purposes.
BTW, it probably doesn’t make sense for the Binding.Mode to be TwoWay, because you will probably not be modifying the Image.Source property dynamically and expect the Data property to be updated correspondingly. It’s possible, though, if that’s what you really want to do.