# stepic - Python image steganography
# Copyright (C) 2007 Lenny Domnitser
#
# 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 2 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, write to the Free Software Foundation, Inc.,
# 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
'''Python image steganography
Stepic hides arbitrary data inside PIL images.
Stepic uses the Python Image Library
(apt: python-imaging, web: ).
'''
__author__ = 'Lenny Domnitser '
__version__ = '0.4'
import warnings
try:
import Image
except:
warnings.warn('Could not find PIL. Only encode_imdata and decode_imdata will work.',
ImportWarning, stacklevel=2)
__all__ = ('encode_imdata','encode_inplace', 'encode',
'decode_imdata', 'decode',
'Steganographer')
def _validate_image(image):
if image.mode not in ('RGB', 'RGBA', 'CMYK'):
raise ValueError('Unsupported pixel format: '
'image must be RGB, RGBA, or CMYK')
if image.format == 'JPEG':
raise ValueError('JPEG format incompatible with steganography')
def encode_imdata(imdata, data):
'''given a sequence of pixels, returns an iterator of pixels with
encoded data'''
datalen = len(data)
if datalen == 0:
raise ValueError('data is empty')
if datalen * 3 > len(imdata):
raise ValueError('data is too large for image')
imdata = iter(imdata)
for i in xrange(datalen):
pixels = [value & ~1 for value in
imdata.next()[:3] + imdata.next()[:3] + imdata.next()[:3]]
byte = ord(data[i])
for j in xrange(7, -1, -1):
pixels[j] |= byte & 1
byte >>= 1
if i == datalen - 1:
pixels[-1] |= 1
pixels = tuple(pixels)
yield pixels[0:3]
yield pixels[3:6]
yield pixels[6:9]
def encode_inplace(image, data):
'''hides data in an image'''
_validate_image(image)
w = image.size[0]
(x, y) = (0, 0)
for pixel in encode_imdata(image.getdata(), data):
image.putpixel((x, y), pixel)
if x == w - 1:
x = 0
y += 1
else:
x += 1
def encode(image, data):
'''generates an image with hidden data, starting with an existing
image and arbitrary data'''
image = image.copy()
encode_inplace(image, data)
return image
def decode_imdata(imdata):
'''Given a sequence of pixels, returns an iterator of characters
encoded in the image'''
imdata = iter(imdata)
while True:
pixels = list(imdata.next()[:3] + imdata.next()[:3] + imdata.next()[:3])
byte = 0
for c in xrange(7):
byte |= pixels[c] & 1
byte <<= 1
byte |= pixels[7] & 1
yield chr(byte)
if pixels[-1] & 1:
break
def decode(image):
'''extracts data from an image'''
_validate_image(image)
return ''.join(decode_imdata(image.getdata()))
class Steganographer:
'deprecated'
def __init__(self, image):
self.image = image
warnings.warn('Steganographer class is deprecated, and will be removed before 1.0',
DeprecationWarning, stacklevel=2)
def encode(self, data):
return encode(self.image, data)
def decode(self):
return decode(self.image)