The problem is that Image::Resizer creates a new default image into which it resizes the original. It takes no account of the attributes--truecolor .v. palette; transparancy color etc.--of the original image.

It could (should) query these attributes of the original image and use them to create a compatible image before performing the copyResize(). Something like this (untested) might do the trick:

sub resize {
    my $self = shift;
    my ($width, $height, $constraint) = @_;
    unless ( defined $constraint ) { $constraint = 1; }
    unless ( $width && $height ) { croak "Image::Resize->resize(): usa
+ge error"; }

    if ( $constraint ) {
        my $k_h = $height / $self->height;
        my $k_w = $width / $self->width;
        my $k = ($k_h < $k_w ? $k_h : $k_w);
        $height = int($self->height * $k);
        $width  = int($self->width * $k);
    }

    my $image = GD::Image->new($width, $height, $self->truecolor ); ##
+ modified
    $image->transparent( $self->transparent() ); ## Added
    
    $image->copyResampled($self->gd,
        0, 0,               # (destX, destY)
        0, 0,               # (srcX,  srxY )
        $width, $height,    # (destX, destY)
        $self->width, $self->height
    );
    return $image;
}
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