OpenCV watermark filters sometimes have black borders.

* 水印处理之前的照片

<img width="2480" height="3508" alt="Image" src="https://github.com/user-attachments/assets/47789e75-7af4-4803-8c7f-19a9de9e7a45" />


* 水印处理后有黑框

<img width="2480" height="3508" alt="Image" src="https://github.com/user-attachments/assets/2cd055ea-b349-46f9-8a19-e72b89cf9bf6" />