This will show you how to store any type of file on an audio cassette. Depending on whether you modify the cassette recorder or not, you can get around 1.5 megabytes on a tape. I can get this much space because I increased the speed of the motor inside the recorder to its maximum by jamming a piece of tin foil in the hole at the back of the motor. I also change the sample rates in Audacity to 132300Hz which lets me write the files to the tape much faster. When I record the files, they are recorded at 132300Hz and then the rate is set to 22050 to slow it back down to the rate at which the program can decode it. These modifications are not needed though if you are just experimenting with small files.

You will need:

A cassette recorder with a line in or microphone socket

KCS08 an old program which converts the file into sound for storing. I can not find this program on line anywhere now so I have uploaded it here.
Here is a website with a detailed description of the software:
ftp://ftp.taygeta.com/pub/forth/compilers/native/dos/DXForth/kcs08.txt

The picture of the program will show you what parameters are available.

Audacity
http://audacity.sourceforge.net/

An audio cable to connect the cassette recorder to the line in socket on the computer

KCS Tape Program.zip
Download

Step 1: Encoding Files to Wav

In the attached zip file on the intro, you will find the program. To encode the included bitmap image, simply double click on encode.bat. The program will then create a wav file.

To edit the batch file, right click it and select edit.
Here is what is currently in the file:
KCS -M -Y -U -L5 1.bmp 1.wav

To encode something with a different name or extension, change the 1.bmp which is the input file, and 1.wav which is the output file to a file name of your choice.

Step 2: Recording the Wav Files to Tape.

Open the wav file with Audacity and set the system volume to full. Connect the earphone socket from the computer to the line in on the cassette recorder. Press record and wait a few seconds. Press play in Audacity and wait until the file ends. Stop the recorder a second after the file ends.

Step 3: Reading and Decoding the Files

To get the files off the tape, you need to connect the earphone socket on the cassette recorder to the line in or microphone socket on the computer. Once you have done this, go into the sound properties in the volume control in Windows and select your recording device. Once you have the settings open, select listen to this device in the listen tab. Set the project rate in Audacity to 22050, Rewind the tape, press record in Audacity and press play on the cassette recorder. Adjust the cassette recorder volume until it is near the top of the sound trace in Audacity. Do not make it too high. After adjusting the volume, rewind the tape, discard the current recording and record the whole thing into Audacity at the same level. Once done, save it as a wav file under the same name as is in the batch file. In this case it is 1.wav. Run decode ignore errors.bat and wait while it decodes. Once it is done, you should see your output file in the same folder as KCS08.

Here is what is inside decode ignore errors.bat
Just change 1.wav and 1.bmp to names of your choice.
KCS -Y -U 1.wav 1.bmp