I have been working with photoshop everyday for the past 8 years and am pretty proficiant with it - if this is a photoshopped pic it was done unbelievably good... very hard to replicate what is seen here
Especially the lighting... notice how the light source is hitting the back foot of the fox (the one in the air), but the light is not hitting his rump/tail area, this is because these areas are in the shadow of the oncoming eagle. The front paws of the fox are on the ground and therefor in the snow.
Very cool pic! Also looks as though it could be a younger fox, making the eagle appear bigger - and golden eagles always look bigger when they have their wings open - they can have a wing span of over 6 ft.