#!/usr/bin/perl
use warnings;
use strict;
use Image::Magick;

my $image = Image::Magick->new;
umask 0022;
my @pics= <*.jpg>;
#my @pics= <*.jpg *.gif *.png>; #add all your extensions here
   
foreach my $pic (@pics){    
   my ($picbasename) = $pic =~ /^(.*).jpg$/;
   my $ok;
   $ok = $image->Read($pic) and warn ($ok);
   my $thumb = $picbasename . '-t.jpg';
   $image->Scale(geometry => '100x100');
   $ok = $image->Write($thumb) and warn ($ok);
   undef @$image; #needed if $image is created outside loop
   print "$pic -> $thumb\n";
}