Koi - a GIMP image authentication plugin
    Copyright (C) 2010  ben howard

    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program.  If not, see <http://www.gnu.org/licenses/>.

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Project Goal Statement
Koi will be a GIMP plugin able to identify manipulation artifacts in an image, highlight modified areas and return a percent chance of forgery by June 2011. 
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Installing Koi on Ubuntu with GIMP 2.6

source: http://github.com/possiblyphilip/Koi
(prebuilt binary also available)

//for local Koi install
sudo apt-get install libgimp2.0-dev
//extract Koi source into a directory 
//while inside Koi source directory 
gimptool-2.0 --install Koi.c 

OR 

//for global Koi install
sudo apt-get install libgimp2.0-dev
//extract Koi source into a directory 
//while inside Koi source directory 
sudo gimptool-2.0 --install-admin Koi.c

OR

//copy Koi.exe into /usr/lib/gimp/2.0/plug-ins/

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Using Koi in GIMP

open an image in GIMP.

select the layer in the image you want to analyse.

open Koi: Tools>Koi

Check the box corisponding to the algorithm(s) you want to run.
Adjust parameters if needed.

Click 'OK' to analyse the image.

Text analysis of the image will be printed to a log file in the directory where the image is stored.
Koi will produce layers highlighting different features of the image in GIMP.

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current screenshots

http://picasaweb.google.com/possibly.philip/koi

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Koi is a system that can identify and highlight image manipulation artifacts. In a world of digital media, every image is suspect of forgery. Koi can put to rest the fear publishers, news agencies , insurance agencies and anyone else who may depend on digital images. Front page news has had its share of embarrassing forgeries published. Some companies have forged images for public relations campaigns which news media picked up, individuals fake images for media attention or to defraud insurance companies. Images “photoshopped” for fun have ended up being the center of news media attention only to be discovered as fakes. With Koi in place an image can be properly inspected for signs of forgery before it is published. With digital images becoming ever more popular, police and other law enforcement agencies need to be able to verify whether images have been altered for use in court as evidence. With forgery running rampant, publishing verified content is a huge edge in the information age. Whenever an image is digitally altered, the software doing the modification changes the original image in ways that may not be detectable to the unaided eye. By applying filters, running transforms and other proprietary Koi algorithms on an image, the modifications can be highlighted and exposed. Every contact leaves a trace – Koi can find it.