Zero-Watermarking Algorithm for Medical Image Based on VGG19 Deep Convolution Neural Network

Table 6

The images under spherical distortion attack.

	Medical image A	Medical image B	Medical image C	Medical image D	Medical image E
The smallest NC value	0.87166	0.74704	0.93512	0.93769	0.62984
The restored watermarking image
Medical image to be tested