At these distances , planets are all dots to the human eye . They have no measurable diameter , they ' re just point sources of light . For a camera that compresses the eye ' s field of view on to a phone screen or computer screen , the situation is even worse . You shouldn ' t except to see differences in size , except through a telescope . What you will see through the eye or camera is a difference in brightness , and indeed Earth is much brighter from Mars than Mars is from Earth . Just as expected . However , your perception of brightness requires some reference point to compare to . In a photograph you don ' t really have any reference . Provided the photo is of good quality , and provided it includes some stars of known magnitude , you could indeed determine the brightness of Earth from a photo taken on Mars . But you ' d need some math .