A blind image watermarking algorithm based on key entropy using the dual-tree complex wavelet transform(DTCWT) and the scale invariant feature transform(SIFT) is proposed in this paper.Firstly,the image feature point is extracted by using the SIFT when generating local invariant circular regions in watermark embedding.Secondly,each circular region is normalized and the entropy of each circular region is calculated,whereas the circular regions which its entropy is greater than average entropy,are...