It depends.
Is the white area just an overly larger white rectangular canvas around the actual object that can easily be cut-off ? Then Image – Trim (combined with Actions) is your friend, like Eric Segeren also explained. Note: any slight variation in the white (like with JPEG compression artefacts) disturbs this process.

Or is it an irregularly shaped white background that needs to be removed ? Then the Magic Eraser might work fine (check its tolerance), but this requires manual sampling and can't be an automated process. And any slight shadow or soft border (hair, fluffy clothes, etc.) will also require extra attention.

Oorspronkelijk geplaatst op Quora: What's the most efficient way to remove variable amounts of white space from a large amount of images in Photoshop?"