Heard has previously claimed she and Depp were having an argument when he approached Whitney on a landing between two staircases in their home in Los Angeles - and she feared he might push her, so hit him in the face.
He added: 'I do remember taking that photograph, which now I know isn't the photograph that I took but a photograph was taken which was very similar to that photograph.
Ms Wass admitted that Heard did hit Depp but only in defence of her sister.
Advertisement He added: 'If you are 20 feet away, in my opinion it can be difficult to see a tear on one's face but it's clear if there is an injury of any type, you would be able to see.