Super User is a question and answer site for computer enthusiasts and power users. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

I sometimes get files from my clients that have the wrong file extension. For example, the name is image.jpg but the file is actually a TIFF image. In many cases I can clarify it by opening the file in a text editor, looking at the first few bytes, then deducing which file type it is.

This works for me with JPEG, TIFF, GIF and PDF files. However there are many more file types out there.

Is there a possibility to automate identification of the correct file type by analyzing the containing data?

share|improve this question

closed as off-topic by random Oct 24 '14 at 14:47

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "Questions seeking product, service, or learning material recommendations are off-topic because they become outdated quickly and attract opinion-based answers. Instead, describe your situation and the specific problem you're trying to solve. Share your research. Here are a few suggestions on how to properly ask this type of question." – random
If this question can be reworded to fit the rules in the help center, please edit the question.

For those interested the file command does this on *nix machines. – boehj Apr 24 '11 at 12:37
Very nice question! Something that I had secretly wanted all this time, but always forgot to ask :) – pepoluan Apr 24 '11 at 13:54
I think linux distributions can detect file extensions – user Apr 24 '11 at 17:11
I do not understand why this question is off-topic (after 3 years). I do not ask for a specific software (i reworded my question to underline this). I just aks for a solution. – Martin Dec 22 '14 at 10:13
I don't understand why 26 people think that boehj *nix-related comment above "adds something useful to the post". This question is tagged windows, but the comment imply: "You can't do that on Windows, you must use *nix instead". So? The comment is directed "for those interested". In what? Change computer? :( – Aacini Sep 8 '15 at 14:47
up vote 112 down vote accepted

You can use the TrID tool which has a growing library of file type definitions for identifying files with.


Wildcards are supported, so in your example you could just put all the images to be examined in a folder, e.g. C:\verifyimages - then you can use the command:

trid C:\verifyimages\*

This will examine all files in the verifyimages folder.

There is also a GUI version available, TrIDNet:


There is documentation available on how you can you can easily integrate TrID or TrIDNet into Windows Explorer and Total Commander:

Windows Explorer

Total Commander

share|improve this answer
Very nice! Thanks for the info! – pepoluan Apr 24 '11 at 13:54
Thanks, this is exactly what I was looking for! – Martin Apr 26 '11 at 13:35
Do note that it indicates it is not licensed for commercial use, only personal use – Chris Magnuson Jan 31 '15 at 17:31
I had some trouble figuring out which download files were necessary to use this program. So this comment is to aid in that. You'll need to download two files. First, either the command line utility or the GUI utility. Second, a folder of XML definitions called "TrID XML defs". Place the definition XML files in the same directory as TrID. Then scan definitions. Finally you can start using it. – mrtsherman Mar 26 '15 at 15:40
Great program. Donated too. – Matthew Lock Feb 1 at 6:19


File tests each argument in an attempt to classify it. There are three sets of tests, performed in this order: filesystem tests, magic number tests, and language tests. The first test that succeeds causes the file type to be printed.

The type printed will usually contain one of the words text (the file contains only printing characters and a few common control characters and is probably safe to read on an ASCII terminal), executable (the file contains the result of compiling a program in a form understandable to some UNIX kernel or another), or data meaning anything else (data is usually “binary” or non-printable). Exceptions are well-known file formats (core files, tar archives) that are known to contain binary data.

share|improve this answer
file is standard, but on older systems (especially non-Linux) not very knowledgeable. For Ubuntu etc it should be quite respectable and even installed as standard. – Thorbjørn Ravn Andersen Apr 24 '11 at 13:28
@Anm_LA, it isn't standard at all on Windows, but the link in the answer is to a port of the GNU version of file to Windows. If other *nix commands are interesting to you as a Windows user, then poke around that site to find all kinds of gems. – RBerteig Apr 24 '11 at 19:54
I very much doubt that file is an expert on files made by Windows applications. – Robin Green Apr 24 '11 at 20:23
@Robin: You're welcome to test it. – Ignacio Vazquez-Abrams Apr 24 '11 at 20:27
@Robin: I very much doubt you've used file at all, and yet you've almost made up your mind about its effectiveness. – tzot Apr 24 '11 at 23:24

I used to work for the French National Library, to build an digital archive system that contains not only digitized books but also millions of digital artefacts with all kinds of strange file types. We used JHOVE to recognize file formats.

JHOVE is open source, it is maintained by JSTOR and the Harvard University Library. It is rather simple to use.

share|improve this answer
cool! but does it recognize proprietary formats like TrID does? anyways, I do have some uses to identify subformats/variants of non-proprietary formats (or, to be precise, proprietary 'extensions' to standardized formats), so this would come in handy. thank you for the heads-up! – pepoluan Apr 24 '11 at 14:00

I use Oracle's OutsideIn libraries in my programs. Not free, but they work well, especially for images. The market-speak says it supports over 500 file types.

share|improve this answer

Not the answer you're looking for? Browse other questions tagged .