Things dont work like that. Any information or image that dont comes from a reliable fount of source is de-confirmed by default.
Just like the God existance debate, atheist are not supposed to proof that God is false, religion must proof that God is real.
I don't think looking at confirmation/deconfirmation should be done in black and white, but rather an estimate of the likeliness. In the first five minutes of that image being shown it being real seemed, by most estimates, fairly unlikely. Most assumed that within the hour, or afternoon/evening, or some period of time, it would be shown to be false like most other leaks. When those points passed in time people began to consider it more likely based on past evidence that image leaks don't tend to be believed for very long because they are relatively easy to show to be false. As more time passes more people will begin to increase their estimate of the likelihood it's valid.
On top of this argument, we also need to consider both realities in comparison and use that to guide our thoughts. This might not be well worded and so I apologize, but consider the reality that Palutena is real. What does this mean?
It means Palutena's model and idle animation is in a similar state of polish as the characters revealed so far. This is not terribly surprising; if they plan to release the game within a year then the vast majority of the models should be nearly finished or at least useable, even if some textures or animations may be missing. People have noted that it becomes likely that the game is in Beta, which is definitely not impossible by the current timeframe. It also means that, clearly, Palutena is playable; how realistic this is in your mind will change how likely the leak is.
In the reality this image is fake, it means a person or group of people spent enough time doctoring two images that the it could fool the entire set of people analyzing the image, some of which have gone to ridiculous extremes to do. It says nothing for her likelihood in the game, as if the image is false then it has nothing to do with the game; her odds do not change. It also gives us no more information.
So which is more likely? I would argue someone with that degree of skill putting that degree of effort in to doctor a picture is VERY unlikely. By comparison, given that Namco is working on this project Nintendo's normal leak strategies might not be functioning to their usual degree. Even if they are not Nintendo has had leaks in the past, it is just unusual. It's also worth noting that people who leak things very rarely leak everything, as they hope that a small leak might be a) forgiven, b) overlooked by their bosses, and c) hard to pinpoint who actually leaked it within the company. It's also much easier to snap one or two pictures than ten. The timeframe component of my assumptions on the part of it's real seems very reasonable given we already have 17 characters who are in a similar state of polish. I also don't find Palutena that unlikely; she could definitely bring some uniqueness to the cast; at very least it's another character who has a shield, something Link was unique for before and he barely used it. As noted by others her laser beams are also a good fit, and I think she'd be more or less popular worldwide, unlike some characters (Black Shadow, Ridley) who are only really popular in certain parts of the world.
Because of this, I think it's more likely real than fake. I'm not going to touch on the god debate at all, that's a topic way to sticky for this thread. I'll stick to the titular goddess instead.