when messgaes are hiden in pictures/ files, most common steg programs leave a common signature that steg searchers use to identify a hiden message in file,

Im not sure if there is a list of these availiable, If anyone knows of one can they show me?

you could download common ones and play about and create a program that looks for certain things, thats what ive been doing, (havent worked on it for ages cos been building a robot arm) in python, mine was going to use common things in the english lang to search for them, this would only work for plain text and not for encrypted files

i2c