what type of hash function are used for SECURE Image steganography ?

MY paper problem is here this is my encoding method- - 1.input a text, 2.detect the edge of the input image by robert mathod & use these pixel as the hash key, 3.read a text and store the data in array list(Lc), 4. the hash function uses the hash key and text data to generate a pattern i.e. sequence of hash value where data will be stored. 5.generated pattern is stored in the array list Lp. 6.the ASCII value of Lci IS REPLACED with blue byte of Lp. 7.the output is the encoded image. MY main problem in this i have not understand what type of hash function used for this purpose,because in paper clearly not mentioned?please suggest me sir