How to check an image's format in Elixir

Question

So let's assume I have a file stored somewhere and it can be either a jpeg file or a png file, what is the way to check what it is?

Should I simply check the extension? Or should I read the file's binary signature? Or how do I do it?

Answer 1

Update: 4/2/2016 to include .JPG validation.

There's a fairly popular hex package Arc that might work for you. Extracted from Arc:

def validate({file, _}) do
  ~w(.jpg .jpeg .gif .png .JPG) |> Enum.member?(Path.extname(file.file_name))
end

Answer 2

I guess you could extract the Magic number of the file and analyse it. That's fairly simple once you have the format specs