How to apply invisible watermark on image block-wise?

Assalam o Alaikum. There is an image on which I have to apply watermark image. Firstly, I have to make blocks of original image and then apply the watermark. Original Image is 256x256 while watermark is 64x64 and total blocks are 4 . each block is with 64x64 size. I don't know how to apply loops. I have implemented block processes method also but image quality is too bad which is not required. I am badly stuck here. Help, please.

[Walter Roberson]

http://www.mathworks.com/matlabcentral/answers/6200-tutorial-how-to-ask-a-question-on-answers-and-get-a-fast-answer

http://www.mathworks.com/matlabcentral/answers/8026-best-way-s-to-master-matlab

[OCDER]

Invisible watermark seems like a fairly advanced topic...

https://petapixel.com/2017/12/22/imatag-uses-invisible-watermarks-protect-photos/

"I don't know how to apply loops."

https://www.mathworks.com/help/matlab/matlab_prog/loop-control-statements.html

[Walter Roberson]

There are some who would claim that an invisible watermark is, by definition, not a watermark. Whether information stored as part of an image is visible or not is pretty much the deciding difference between whether you are doing "watermarking" or "steganography". There have been rather a lot of postings about steganography.