Answer

1. Create a string field with the value of a string for example:"Boat"
2. Change the Marks card to shape and placed this new field on Shape.
3.  Add the image as a custom shape. For more information, see Shape Properties
4. Click the Shapes button on the Marks card and select the custom shape as the value for "Boat".
5. Optionally, change the size of the shape by using the size button the marks card. The size of the cell itself may also need to be adjusted.
6. Edit the tooltip for this view by clicking tooltip on the Marks card.
7. Place the new sheet on the dashboard.