I thought I posted the final version of this. I've been reading as I come here and noticed that it's a possibility that if your thread dithers on too long, someone might just cut it off. I don't know whether that happened, or I just forgot to click the create button, but I don't think a thread has finished until one has a version with a bit of polish:

$ perl tg6.pl
downloaded 83 images from http://www.yahoo.com
to folder site_4
$ cat tg6.pl
#!/usr/bin/perl -w
# creates a new directory and downloads images from url to it
# perlmonks node 965537; thx aaron and A.M.
use strict;
use feature ':5.10';
use WWW::Mechanize;
use LWP::Simple;
use Errno qw[ EEXIST ];

# get information about images
my $domain = 'http://www.yahoo.com';
my $m = WWW::Mechanize->new(); 
$m->get( $domain);
my @list = $m->images();

# create new folder and download images to it.
my $counter = 0;
my $dir = &mk_new_dir;
for my $img (@list) {
  my $url = $img->url_abs();
  $counter++;
  my $filename = $dir. "/image_". $counter;  
  getstore($url,$filename) or die "Can't download '$url': $@\n"; 
}

# output
print "downloaded ", $counter, " images from ", $domain, "\n";
print "to folder ", $dir, "\n"; 

sub mk_new_dir {
  my $counter2 = 1;
  while(1){
    my $word = "site";
    my $name = $word . '_' . $counter2++;
    if( mkdir $name, 0755 ){
      return $name;  # success, return new dir name
    } else {
      next if $!{EEXIST}; # mkdir failed because the file exists
      die $!;             # it failed for some other reason; bail out!
    }
  }
$
[download]

I think aaron's integrating the 'mkdir $name, 0755' as the truth condition of the sub is great, as well as the post-increment of $counter2 to drive the thing forward.