Drag, Drop and Move Around Images

Question

I'm creating an interface that allows users to drag an image from outside the program and drop it into an imageview within a gridpane.

Currently, the interface is able to handle drag and drop photos, but once its dropping and I cannot move it again.

@FXML
void imageViewDragDropped(DragEvent event) {
    Dragboard dragboard = event.getDragboard();
    if (dragboard.hasImage() || dragboard.hasFiles()) {
        try {
            photoImageView.setImage(new Image(new FileInputStream(dragboard.getFiles().get(0))));
        } catch (FileNotFoundException e) {
            throw new RuntimeException(e);
        }
    }
    event.consume();
}

@FXML
void imageViewDragOver(DragEvent event) {
    Dragboard dragboard = event.getDragboard();
    if (dragboard.hasImage() || dragboard.hasFiles()) {
        event.acceptTransferModes(TransferMode.COPY);
    }

    event.consume();
}

How do edit the copied code to allow the photo that has been dragged and dropped to be move again?