@kaushik25,
The chart contains multiple Canvas elements, in which the topmost Canvas element is being exported while saving/copying the image using the browser’s right-click. However, you can create a custom contextual menu and add exportChart method to export the chart as an image using right-click.
Kindly take a look at this JSFiddle for an example on the same.
—
Adithya Menon
Team CanvasJS