There is to my mind a considerable physical similarity, in terms of build, eyes, face bone structure (especially the eyes and jaw) and colouring; although Knightley, not spending much of her time on the west coast of the USA with very few/no clothes on, is paler. But there is a greater similarity in their expressions, especially when they smile or open their mouths, or bite their bottom lips. All pornstars do this, but on Tori it looks playful, minxy and slightly vulnerable, just as it does on Knightley. On balance I'd have to favour Knightley though; physically Tori is sexier and I'm sure she'd be better in bed and could do amazing things with a cock, but Knightley has more class. There's something about having been fucked in all sorts of ways by hundreds of different men and/or women on camera in return for sums of money that does irreparable damage to one's reputation. Plus Knightley can actually act.