use 5.020;
use warnings;
use File::Copy;

my $in_dir  = '/tmp/foo';
my $out_dir = '/tmp/bar';

opendir(my $dir_handle, $in_dir)
    or die "Can't open directory '$in_dir': '$!'\n";
my @files = readdir($dir_handle);
closedir $dir_handle;

# Eliminate entries starting with '.'
@files = grep { $_ !~ /^\./ } @files;

# Split the file names in their numeric and non-numeric part
my @unsorted = map { [/^(\d+)(.*)/] } @files;

# Sort by numbers first, non-numeric part second
my @sorted = sort { $a->[0] <=> $b->[0]  or
                 $a->[1] cmp $b->[1] } @unsorted;

# ...and re-build the filenames, re-using our old array
@files = map { $_->[0] . $_->[1] } @sorted;

# Finally, copy the stuff
my $file_number = 1;
for my $file(@files) {
    copy("$in_dir/$file", "$out_dir/${file_number}.gif")
        or die "The copy operation for '$file' failed: '$!'";
    $file_number++;
}