In one of my sites I have been using the following function for a while (uses Image::Magick):

use Carp;
use Image::Magick;
...
# makethumbnail( jpeg-data )
# creates a thumbnail with maximum size 120x120
sub makethumbnail {
    my $data = shift;
    my $image=Image::Magick->new(magick=>'JPEG');
    my $res;
    $res = $image->BlobToImage($data);
    if ($res) {
    carp("makethumbnail: Error reading image - $res\n");
    return undef;
    }
    $res = $image->Transform(geometry=>'120x120');
    if ($res) {
    $res = $image->Resize(geometry=>'120x120');

    if ($res) {
        carp("makethumbnail: Error while resizing: $res\n");
        return undef;
    }
    }
    my @blob = $image->ImageToBlob();
    if ($#blob!=0) {
    carp("makethumbnail: Error while converting to blob\n");
    return undef;
    }
    return $blob[0];
}
[download]

I seem to recall that the double command for resizing depends on the interface changing at some point.

Cheers
Antonio

Update: I hadn't read the original post carefully enough. Of course you were asking for a non-Image::Magick solution. Hopefully someone will find this helpful anyway.

The stupider the astronaut, the easier it is to win the trip to Vega - A. Tucket