How do I tell if someone's faking a filetype? (PHP)

Question

I\'m programming something that allows users to store documents and pictures on a webserver, to be stored and retrieved later. When users upload files to my server, PHP tells m

Answer 1

On a unix system, capturing the output from the 'file' command should provide adequate info.

Answer 2

Magic number. If you can read first few bytes of a binary file you can know what kind of file it is.

Answer 3

Check out the FileInfo PECL extension for PHP, which can do the MIME magic lookups for you.