IANA image format string from binary stream

Question

How can I get the official IANA Image Media Type (if any) of a binary stream? I'd like to avoid trusting to file extensions and vague guesses when handling images. Preferably some command using common tools like ImageMagick's identify, or some programming language if necessary.

Answer 1

You could use the file command. It's available on most linux distributions by default, and you can get it for Windows via the GnuWin32 file package.

Call it with:

$ file --mime-type clock.png 
clock.png: image/png

Note that it's not 100% accurate - I don't think anything can be theoretically.

If you want to do that in code, there's libmagic that provides a C api. It can process either files or in-memory buffers. (file uses that on Linux.)