Although I take leaks very lightly, this Falco image seems like it could create good discussion.
There are some noticeable differences in the two images:
I've rotated the image to better compare it to the "leaked" Falco.
Clearly there are some differences like facial expression, lighting of the "headgear", and color scheme, but you can pick some smaller details out of the two. In the "leaked" image Falco has smaller pupils, less "eyeliner", he has more detailed feathers on the lower half of his head. Additionally, his neck area looks much better, and there are some jacket differences.
However, one of the things that to me raises some red flags is that the feathers on the upper half of his head looks to be the same shape, if not identical.
If it is fake, it was a smart move by the leaker because we can assume the SF reps will look similar to their Brawl counterparts. However, those little details within the image make me wonder... is it real? Or does this person just have some good photoshop skills to make me go... "hmmm..."