How to identify contents of a byte[] is a JPEG?

Question

I have a small byte array (under 25K) that I receive and decode as part of a larger message envelope. Sometimes this is an image, furthermore it is a JPG. I have no context

Answer 1

From wikipedia:

JPEG image files begin with FF D8 and end with FF D9.

http://en.wikipedia.org/wiki/Magic_number_(programming)