You are wrong.
Stepic doesn’t work for JPEG files(http://domnit.org/blog/2007/02.html).
The reason: JPEG are not lossles format.
Your program runs because you use the same variable to decode (without read the file another time). If you don’t beleave me, try this:
import Image
import stepic
im = Image.open(’in.jpg’)
s = stepic.Steganographer(im)
im2 = s.encode(’This is some cool text’)
im2.save(’out.jpg’,’JPEG’)
im3 = Image.open(’out.jpg’)
s = stepic.decode(im3)
data = s.decode()
print data

I tried following with the stenography code provided in your site.

- opened a binary file
- read few lines
- wrote those files in the image file opened
- tried to decode

But it couldn’t decode that. Does this code work for binary content as well? I got the following error:
File “”, line 1, in
UnicodeDecodeError: ‘ascii’ codec can’t decode byte 0xc3 in position 12: ordinal not in range(128)

Regards,
Vkm

640×480 should be enough for small text. Each character is spread across 3 pixels.

You’re probably having trouble with the command line because you are saving JPEGs. Since JPEG is lossy, it doesn’t preserve the exact values Stepic uses. A good output format for Stepic is PNG–if that makes the files too large, this type of steganography is probably not right for the application.

Yep, I assumed you got the link from Daily Python URL, since that link Xtupled traffic to my site, where X is a single digit number that depends on what metric you look at.

Have you read the explanation of how Stepic works?

Man, That was quick. The two of us are probably the only two in the whole webosphere that used the word “Steganography” today!!!

I was thinking that maybe you could pass in an MD5 hash an that the get next pixel method would use that to determine where it would go next. There would be no guarantee that an allready modified pixel would not be remodified but the chances and consequences would be low.

The images are 640×480 and the amount of text is low. How much is possible.

Have a look at the command line as that didn’t work for me. I didn’t investigate at it may well have been my problem

Well done anyway and thanks for the code and the tip. BTW, I got the link off the PIL news page today.

http://www.pythonware.com/daily/

Cheers

Diarmuid

Just a note, if you’re only making 1 image+data for each input image, you don’t have to manually make a Steganographer instance. You can just do im2 = stepic.encode(im, 'This is some cool text').

If you’re using this in an automated production environment, are you guaranteeing that the images are large enough to store the data?

I haven’t been actively changing the code (I think it’s stable, but there are some TODOs I haven’t touched). If you find any bugs, I’d happily take bug reports or patches.