How can I determine a file's true extension/type programmatically?

Question

I am working on a script that will process user uploads to the server, and as an added layer of security I\'d like to know:

Is there a way to detect a file\'s true e

Answer 1

Is checking the MIME type simply enough? I am assuming that changing the extension on a file doesn't change it's MIME type?

Is MIME type a strong enough indicator to go by here?

Thanks for all of the responses thus far.