how i can make a part of image black

I would like to crop an image that is, make a small block of an encrypted image black. How can i do that?

Answer 1

[Image Analyst]

First, decrypt it, then set the block to black (zero)

yourImage(row1:row2, column1:column2, :) = 0;

Or crop it

yourImage = yourImage(row1:row2, column1:column2, :);

Then encrypt it again if you need to.