C# How can I test a file is a jpeg?

Question

Using C# how can I test a file is a jpeg? Should I check for a .jpg extension?

Thanks

Answer 1

The best way would to try and create an image from it using the Drawing.Bitmap (string) constructor and see if it fails to do so or throws an exception. The problem with some of the answers are this: firstly, the extension is purely arbitrary, it could be jpg, jpeg, jpe, bob, tim, whatever. Secondly, just using the header isn't enough to be 100% sure. It can definitely determine that a file isn't a jpeg but can't guarantee that a file is a jpeg, an arbitrary binary file could have the same byte sequence at the start.