Tell if file is an image using .Net framework, not by checking magic numbers

Question

With all the smarts of actually loading images being done by the .net framework, seems like I shouldn't have to repeat it all in my code by checking for magic numbers, or using a hack like this:

Private Function IsImage(FileName as String) As Boolean
    Try
        Using img As New Bitmap(FileName)
        End Using
    Catch ex as System.ArgumentException
        Return False
    End Try
    Return True
End Function

Am I missing something obvious, like System.Drawing.IsImage(stream)?

Answer 1

You will need to open up the file and read the relevant headers for the file types you want to support, as mentioned here:

determine if file is an image

I don't think there is anything already in the .NET framework that can do this for you, other than loading it into an image and querying the image format:

Find image format using Bitmap object in C#

An alternative theory (no actual facts to back this one up): perhaps the file in Windows holds meta-data that flags it as an image - in the same manner than the properties dialog seems to show artist information for audio files. This could be a cute way to avoid opening the file.

Edit by FastAl Jun 2020. More useful links:

Using .NET, how can you find the mime type of a file based on the file signature not the extension

Not what I asked for, but here are the magic #s:

https://en.wikipedia.org/wiki/List_of_file_signatures

https://www.garykessler.net/library/file_sigs.html