How to detect if file is an image in perl

Question

In order to set some varaibles i need the information if a given file on my server is an image. I do not know anything about the file exept for its location and name.

Is there a way to detect if a file is an image WITHOUT looking at the file extension?

Answer 1

An easy way to do this is to delegate the work to ImageMagick through the PerlMagick CPAN module. The Identify and Ping methods are designed for that purpose.

use strict;
use Image::Magick;

my $im = Image::Magick->new();

my ($width, $height, $size, $format) = $im->Ping('/path/to/my/image.jpg');

After executing this little program, the $format variable will contain a string with the identified format of the image (in this example: "JPEG"), or undef in case of error (non-existing file, unrecognized format, etc.).

Edit: ...and to completely answer your question: it is probably safe to assume that a given file is an image if Ping returns a format string, and if it is part of whichever subset you decide to white-list from ImageMagick's list of supported formats (which also includes non-image formats).

Answer 2

JRFerguson mentions the command file in a comment attached to the question. It comes with a C library counter-part, libmagic. The Perl binding is called File::LibMagic.

use File::LibMagic qw();
my $detect = File::LibMagic->new;
$detect->checktype_filename("first_success.jpg") =~ /^image/

Expression returns true for image types.

Answer 3

The command file, as first mentioned by @JRFerguson, has limitations versus File::LibMagic, Image::Magick, or Image::ExifTool.

But file is great when you can't install or use those modules. As for sample code, you could go with something like this:

my $file = "/dir/images/image.jpg";
my $type = `file $file`;

unless ($type =~ /JPEG/i
     || $type =~ /PNG/i) {
print "The file is not a valid JPEG or PNG.";
}

The idea is just to regex against the known image formats.