If you didn't notice before, all of them are WAIST DEEP IN THE SNOW!!! Except for Frodo, Sam, Merry, Pippen, and Gimli. They are being carried. Plus, Legolas is the only one on top of the snow and then there are footprints!!!!
As stated before, they were IN the snow and it was SNOWING. Please take into consideration, even without those conditions, Legolas would not have left footprints. If you read the books you would know that elves walk lightly and are able to not leave footprints if need be.
I see footprints in all the scenes except one, the very first snow scene before it starts to snow. But since yes, it's an overhead shot and we're watching from pretty high up, I don't think we can see the footprints.
Thinking this slipup through, how could it be possible after all? They didn't just drop the actors from a helicoptor. They had to actually be walking through snow for a little while at least. If that shot was done on computer, surely the animators wouldn't forgot something as obvious as footprints in snow!