Firstly, it came from a Facebook account that is unverified, even though it has thousands of followers.
Let's also look at the side profile. Clearly not Jennifer Aniston.
A simple Google search also reveals that the exact same picture has been all over Pinterest for about a year.
In fact, we've found out exactly where the dress is from. It's from an Israeli label called Dimitrius Dalia and the woman in the picture is a model, seen here in all of the 2014 collection photos.
You can see the picture of Aniston's alleged wedding dress clearly with the exact same stance, leaning against the exact same mirror. On the left is "Jennifer Aniston", on the right is the wedding dress model.
In conclusion: It's not Jennifer Aniston in that photo.
But it is a very nice dress. Maybe one day we'll get to see the real deal. ❤️