How to resist combined geometric attacks effectively and improve the embedded capacity of the watermark has always been a challenging topic in the field of digital watermarking.In view of this situation

a watermarking algorithm that resists combined geometric attacks and has a larger embedded capacity is proposed in this paper.Firstly

feature points from the attacked image are extracted with SURF algorithm

then they are matched with a small amount of feature points of strong robustness

which are extracted from the original image.The matching point pairs are used to estimate the affine matrix accurately and then the geometric attacks are corrected to resynchronize the embedded watermarks.Due to positioning errors introduced during the attacking/correction process

some positioning watermarks are embedded in the spatial domain to improve the accuracy of the resynchronization.Considering the excellent erasure correcting performance of LT codes

the watermark bit sequence is encoded by LT-code such that the anti-cropping performance of the algorithm can be improved.The experimental results show that the proposed algorithm not only has a larger embedding capacity

but also is resistant to the cropping and combined attacks.