#! /usr/bin/perl
use strict;
use warnings;

my $text = do { local $/; <DATA> };
my @matches;

while ( $text =~ m<\\includegraphics(?:\[.*?\])?\{(.+?)\}>gc ) {
    push @matches, $1;
}

{
    local $\ = local $, = $/;
    print @matches;
}

__DATA__
Schau mal dies: \includegraphics{bild1.jpg}
Oder dieses: \includegraphics[2,"second"]{bild2.jpg}
Aber nicht das hier: \includegraphicsNew{no_pic.jpg}