How to remove the background of the images?

Hi,

Below are the sample images.

How to remove the background including both the surface and the shadow in the above image?

How to remove the background and only have the human in the above image?

How to remove the white textile fabric background and only have the things on the table for the above image?

For these types of background removal, do they need to be treated separately or is there an universal algo to deal with the images cleverly?

Please advise.