What is psnr in steganography?

PSNR is one of metrics to determine the degradation in the embedded image with respect to the host image..

Values over 36 dB in PSNR are acceptable in terms of degradation, which means no significant degradation is observed by human eye

[source] Xuanwen Luo, Qiang Cheng, Joseph Tan, "A Lossless Data Embedding Scheme For Medical in Application of e- Diagnosis," Proceedings of the 25th Annual International Conference of the IEEE EMBS Cancun, Mexico. September 17-21, 2003.