The JND (just noticed difference) threshold matrix based on block was calculated by a new human visual model

and then a text encryption algorithm based on image adaptive public watermarking technique operating in DWT domain was presented. Firstly

the text in a file was encoded with Reed Solomon codes for robust and transferred into a binary sequence

which could be permuted randomly to a final watermark. Then

two neighboring blocks were selected from the Hilbert scanning sequence of the host image blocks in turn

and transformed by 1 level DWT. By JND

the final watermark was embedded into the host image by modifying the average values of the two corresponding subbands. The experimental results show that the embedded watermark is invisible to human eyes at a low PSNR

and the algorithm is robust to common image processing operations

especially to signal enhancement. The conclusion is that the algorithm is effective and practical.