ffsteg
Farbfeld image format steganography tool with zero dependencies!!!
Using it is straight forward too...
$ cat in.ff | ./ffsteg enc `echo sitenbay | ./stdin2bin.sh` > out.ff
encoded: 72 bits
$ cat out.ff | ./ffsteg dec 72
011100110110100101110100011001010110111001100010011000010111100100001010
You can also use some handy farbfeld tools to convert it back and forth to png
$ cat in.png | png2ff | ./ffsteg enc `echo ':)' | ./stdin2bin.sh` | ff2png > out.png
encoded: 24 bits
$ cat out.png | png2ff | ./ffsteg dec 24
001110100010100100001010