A new image blind watermarking algorithm based on adaptive quantization step in discrete wavelet transform(DWT) is proposed

which can be used in copyright authentication.In the proposed algorithm

the perceptually significant coefficients are selected from LL subband to be the embedding domain

and a minimum quantization step

which guarantees the invisibility and robustness

is used to quantify the selected coefficients.The binary watermarks are alternately embedded on the different quantified levels by adaptively increasing the quantization step.As a special example

the least 5 bits of the selected coefficients are utilized to express the watermark.Considering the localization character of wavelet transform in spatial domain

a block-based rounding method is adopted to achieve the purpose of precise embedding.As to the detecting algorithm

a novel difference detecting algorithm is created to improve the robustness of system.The experimental results show that the proposed algorithm has the following characters: large information capacity

invisibility and robustness against attacks such as some common image processing operations

lossy compression

cropping and some geometric transformations etc.