Shadows are used depending some aspects like lighting effect, size, dimension and edge of the image. Using blur also adds some more effects to the finalized image. A perfect looking image for any branding, commercial product or print display requires a sharp edge with drop shadow.
A primary image requires some extra features before publishing. For a better and attractve looks of an image, it is necessary to use drop shadow to look like a natural shadow considering the size and dimension of provided image. Using shadow inside and outside of an image makes the original image perfectly ready for your desired purpose.
By adding a shadow effect, illusion of the product can be created which has its depth and solidity relationship with other surface.