use Image::GD::Thumbnail;

my $original = '/Pfad/zum/Originalbild';
my $thumbName = '/pfad/zum/Thumbnail';
open IN, "<$original"  or die "Could not open.";
my $srcImage = GD::Image->newFromJpeg(*IN);
close IN;
# Create the thumbnail from it, where the biggest side is 150 px
my ($thumb,$x,$y) = Image::GD::Thumbnail::create($srcImage,150);
# Save your thumbnail
open OUT, ">$thumbName" or die "Could not save ";
binmode OUT;
print OUT $thumb->jpeg;#$dstImg;
close OUT;