pngtext

A steganography tool to store text or other data inside PNG images.

NOTE: this version (v1.0.1) is incompatible with previous versions

Getting Started

Follow these instructions to build pngtext. These instructions guide on how to build pngtext as a program, but it can also be used as a library.

Prerequisites

You need to have these installed on you machine to build pngtext:

1. the dub package manager
2. a dlang compiler. dmd works, use gdc if you care about speed
3. an internet connection for dub to fetch the dependencies

Building

Run these commands to build pngtext:

dub fetch pngtext
dub build pngtext -c=pngtextapp -b=release #--compiler=gdc # uncomment to use gdc to compile

If the build is succesful, the built binary will be in ~/.dub/packages/pngtext-*/pngtext/
Copy the binary to a path where the shell can find it (could be ~/.local/bin/).

Running Tests

To run the unittests on pngtext run:
dub test pngtext

Using

This describes how to use pngtext.

Writing Data to PNG Image

Text Editor

pngtext comes with a built in simple terminal based text editor. To edit hidden text in a png image, run this:
pngtext path/to/pngImage.png
or:
pngtext editor -i path/to/pngImage.png -o path/to/outputImage.png

Commmands

Aside from text editor, you can also write other types of data using write command:

The following command will read data from stdin and encode it in pngFile.png, and write resulting image to outputPngFile.png:
pngtext write -i pngFile.png -o outputPngFile.png

To read the data from a file, use the --file or -f option:
pngtext write -i pngFile.png -o outputPngFile.png -f fileContainingData

Reading Data from PNG Image

To read data, that was written using pngtext, use the read command:
pngtext read -i pngFile.png

To read the stored data into a file, use the --output or -o option to specify the output file:
pngtext read -i pngFile.png -o outputDataFile

Calculating Maximum Data Capacity from PNG Image

To calculate exactly how many bytes a png image will be able to store, use the size command:
pngtext size -i pngFile.png [-q QUALITY]
This will write the number of bytes pngFile.png can hold if all pixels are used.
Possible values for -q option are below:

• 1 - highest quality - 3 bits per pixel
• 2 - high quality - 6 bits per pixel
• 3 - low quality - 12 bits per pixel
• 4 - zero quality - 24 bits per pixel

1 pixel = 4 bytes = 32 bits
the alpha byte is not used, so transparancy of an image will not be affected