Hi,
it's a bit hard to help you because without the HTML-Code of the Upload-Site (especially the form), we can't test this here. It doesn't look too bad at first glance, though. Are you getting any error messages on the console?

Some thoughts:

print "\nWe found $cnt images";

# don't "use" the module in the foreach loop otherwise it's done each 
+time
use WWW::Mechanize if $cnt > 0; 

unless ($cnt > 0) {
   print "No images selected\n";
   exit 1;
}

my $mech = WWW::Mechanize->new();

foreach my $image (@images)
   $cnt2++;

   print "\n\t Trying picture $currentdir/$image - $cnt2 of $cnt\n";

   $mech->get( $url );

   # do you have the correct form here?
   print $mech->content;

   $mech->submit_form(
      form_number => 1,  # sure? this could be one problem
      fields      => {
          file        => "$currentdir/$image",
          category    => "$category",
          name        => "$name",
          description => "$description"
          }
     );
[download]

If that does not help, I can only - as always - suggest to use Corion's WWW::Mechanize::Shell - it will allow you to interactively fill out the form (on the commandline) and after having done so successfully, automagically print out your steps as valid perl code - for me this is much easier than to write the code in the first place...
Good luck,
svenXY