Start from LSB data hiding in images.

C.K. Chan and L.M. Cheng, Hiding data in images by simple LSB substitution, Pattern Recognition, 37(3) (2004) 469–474.

Our suggestion data hiding in image would be a better choice.

Image hiding by optimal LSB substitution and genetic algorithm

Ran-Zan Wang!, Chi-Fang Lin",*, Ja-Chen Lin!

Here my list of publications will give better idea on image steganography

http://scialert.net/eboardlivedna.php?issn=1812-5638&id=91.1782

Depends on the target. Metadata, image insertion, white space substitution , echo, lsb, spread spectrum, color manipulation, hidden stream are a few of the oldies but goodies

data hiding by LSB substitution using gene expression programming

Marghny Mohamed , Hussein Abul-kasim

I have all the matlab codes for my steganography techniques.

if you need please leave a message beside the relented paper with your email address.

I will be mail you the code.

Thanks

https://www.researchgate.net/profile/Zakir_Khan3/publications

You can also tuck data into a filestream in an existing document

study it

Article Threshold-based Steganography: A Novel Technique for Improve...

Current art data hiding method for digital images are all available on DDE webpage :

http://dde.binghamton.edu/download/

Here you can find matlab code (and C++ for some) of almost all current method for both JPEG and spatial domain and current method for steganalysis as well, using high dimensional feature space.

@Rémi Cogranne: thanks! It is really a good link