I partially blame my math teacher for this stuff... He forced us poor students into similar effects in Mathcad and also claimed Python is loads nicer than Perl :)
Note: This only works for grayscale (Black & White) images. Color palettes for color images is much more complex.
Update: fixed bug in emboss and added invert and level.

#!/usr/bin/perl -w

use strict;
use GD;

sub blur {
my $image = GD::Image->newFromJpeg("image.jpg");
my ($width,$height) = $image->getBounds();
my $image2 = GD::Image->new($width,$height);

for my $w (2..$width-1){
 for my $h (2..$height-1){
  my $index = $image->getPixel($w,$h);
  my (@rgb) = $image->rgb($index);
  my $blur = (
  ($image->rgb($image->getPixel($w-1,$h-1)))[0]+
  ($image->rgb($image->getPixel($w-1,$h)))[0]+
  ($image->rgb($image->getPixel($w-1,$h+1)))[0]+
  ($image->rgb($image->getPixel($w,$h-1)))[0]+
  ($image->rgb($image->getPixel($w,$h)))[0]+
  ($image->rgb($image->getPixel($w,$h+1)))[0]+
  ($image->rgb($image->getPixel($w+1,$h-1)))[0]+
  ($image->rgb($image->getPixel($w+1,$h)))[0]+
  ($image->rgb($image->getPixel($w+1,$h+1)))[0])/9;
  $blur = sprintf("%.f",$blur);
  $blur = $blur > 255 ? 255 : ($blur < 0 ? 0 : $blur );
  $index = $image2->colorExact($blur,$blur,$blur);
  if ($index == -1) { $index = $image2->colorAllocate($blur,$blur,$blu
+r); }
  $image2->setPixel($w,$h,$index);
  }
 }

 open(JPEG,">blur.jpg") || die $!;
 print JPEG $image2->jpeg;
 close(JPEG);
}

sub sharpen {
my $image = GD::Image->newFromJpeg("image.jpg");
my ($width,$height) = $image->getBounds();
my $image2 = GD::Image->new($width,$height);

for my $w (2..$width-1){
 for my $h (2..$height-1){
  my $index = $image->getPixel($w,$h);
  my (@rgb) = $image->rgb($index);
  my $sharpen = 
   5*($image->rgb($image->getPixel($w,$h)))[0]-
  ($image->rgb($image->getPixel($w-1,$h)))[0]-
  ($image->rgb($image->getPixel($w,$h-1)))[0]-
  ($image->rgb($image->getPixel($w+1,$h)))[0]-
  ($image->rgb($image->getPixel($w,$h+1)))[0];
  $sharpen = sprintf("%.f",$sharpen);
  $sharpen = $sharpen > 255 ? 255 : ($sharpen < 0 ? 0 : $sharpen );
  $index = $image2->colorExact($sharpen,$sharpen,$sharpen);
  if ($index == -1) { $index = $image2->colorAllocate($sharpen,$sharpe
+n,$sharpen); }
  $image2->setPixel($w,$h,$index);
  }
 }

 open(JPEG,">sharpen.jpg") || die $!;
 print JPEG $image2->jpeg;
 close(JPEG);
}

sub emboss {
my $factor = shift;
$factor ||= 0;
my $image = GD::Image->newFromJpeg("image.jpg");
my ($width,$height) = $image->getBounds();
my $image2 = GD::Image->new($width,$height);

for my $w (2..$width-1){
 for my $h (2..$height-1){
  my $index = $image->getPixel($w,$h);
  my (@rgb) = $image->rgb($index);
  my $emboss = 
  (-$image->rgb($image->getPixel($w-1,$h-1)))[0]+
  ($image->rgb($image->getPixel($w+1,$h+1)))[0]+$factor;
  $emboss = sprintf("%.f",$emboss);
  $emboss = $emboss > 255 ? 255 : ($emboss < 0 ? 0 : $emboss);
  $index = $image2->colorExact($emboss,$emboss,$emboss);
  if ($index == -1) { $index = $image2->colorAllocate($emboss,$emboss,
+$emboss); }
  $image2->setPixel($w,$h,$index);
  }
 }

 open(JPEG,">emboss.jpg") || die $!;
 print JPEG $image2->jpeg;
 close(JPEG);
}


sub invert {
my $image = GD::Image->newFromJpeg("image.jpg");
my ($width,$height) = $image->getBounds();
my $image2 = GD::Image->new($width,$height);

for my $w (1..$width){
 for my $h (1..$height){
  my $index = $image->getPixel($w,$h);
  my (@rgb) = $image->rgb($index);
  for(@rgb) { $_ = 255-$_ }
  $index = $image2->colorExact(@rgb);
  if ($index == -1) { $index = $image2->colorAllocate(@rgb); }
  $image2->setPixel($w,$h,$index);
  }
 }

 open(JPEG,">invert.jpg") || die $!;
 print JPEG $image2->jpeg;
 close(JPEG);
}

sub level {
my $level;
if (@_) { $level = shift; }
$level ||= 0;
my $image = GD::Image->newFromJpeg("image.jpg");
my ($width,$height) = $image->getBounds();
my $image2 = GD::Image->new($width,$height);

for my $w (1..$width){
 for my $h (1..$height){
  my $index = $image->getPixel($w,$h);
  my (@rgb) = $image->rgb($index);
  for(@rgb) { $_ = $_+$level > 255 ? 255 : ($_+$level < 0 ? 0 : $_+$le
+vel); }
  $index = $image2->colorExact(@rgb);
  if ($index == -1) { $index = $image2->colorAllocate(@rgb); }
  $image2->setPixel($w,$h,$index);
  }
 }

 open(JPEG,">level.jpg") || die $!;
 print JPEG $image2->jpeg;
 close(JPEG);
}


blur;
sharpen;
emboss; #Factor can be passed as argument
invert;
level; #Level can be passed as argument
[download]

Altho this code isn't all that clean and fast, it does the job.
Sample Output is here.

Greetz
Beatnik
... Quidquid perl dictum sit, altum viditur.