How to Paint Shadows
Cast shadows are away from the sun. So to see where to place them in your painting you must first look at where the light is shining from. The shadow will be opposite the direction of the sunlight. There is no great secret with how to paint shadows.
If you are painting from a photograph of an overcast day, and you would like to add more light to your painting, decide on a light source and place your shadows accordingly.
In the picture below you can see both a shadow and a reflection. The reflection is towards the bottom of the image – hence towards the viewer. The shadow is pointing in another direction and is pointing away from the sun.
Both the shadow and reflection are connected to the feet which are on the sand. If the man was jumping with his feet in the air, the shadow and reflection would not be connected to his image.