The embedding is performed in DCT domain using 8x8
blocks by quantizing the DCT coefficients of image blocks. We
select the low frequency coefficients in every image block to
form a vector of host signal where we will embed the QR code
bits. We embed the QR code bits with rate 0.2, means we
embed 1 watermark bit into 5 coefficients. Then we generate a
random spread vector with the same dimension as host-signal
vector and normalize it. After that we quantize the projection of
host-signal vector to spread vector based on the QR code bits
using uniform scalar quantizer.