I would suggest that you first read surveys, like the one I provided to the research community in 2010: "Digital Image Steganography: Survey and Analyses of Current Methods". Signal Processing, Volume 90, Issue 3, March 2010, Pages 727-752.
Image steganography is the procedure of hiding secret information in an image and no one identify if there is a secret information is hide. I can be done by using the LSB bits of the image pixels. In military, it can be used for private communication, so no one can understand the information exchanged by two teams. Better to know please read the paper Conference Paper An Efficient Filtering Based Approach Improving LSB Image St...