SPA (Sample Pair Analysis) method is one of the most effective steganalysis for LSB steganography. It proves that SPA can detect HSBH algorithm in theory and experiment. Experimental results show that the correct rate of detection is nearly 100% when the embedding rate p>3%.And an improved HSBH Algorithm against SPA is presented. After improvement
no matter how much message is embedded
SPA steganalysis will get a very small estimate value and make an incorrect judgment
so attaining the hiding information securely. Finally the applicable range of SPA and the method which can resist SPA steganalysis are concluded.