How can i detect faces and censor(pixelate) it ?

I have a school project and i have 5 days to go to do it.We need to detect faces vision.CascadeObjectDetector and after that we need to censor out the faces.The result should be an image which i add there.

But insted of blurring the face i need to pixel the detected face like this. https://www.google.sk/search?q=censored+face&tbm=isch&source=iu&ictx=1&fir=0Spj2NSDFA1zfM%253A%252Ci7J8rMBqEz4lSM%252C_&usg=__kBDLl6DT7K38L5fdOtn5MfSWjGQ%3D&sa=X&ved=0ahUKEwi3tPfb1MbaAhWEEywKHViBAh0Q9QEIKTAA#imgrc=oZLGM0rP5tnKtM: .My problem is that i dont know how to pixel out the face i have found a source code for detect the faces clear all clc %Detect objects using Viola-Jones Algorithm

%To detect Face FDetect = vision.CascadeObjectDetector;

%Read the input image I = imread('lena512c.bmp');

%Returns Bounding Box values based on number of objects BB = step(FDetect,I);

figure, imshow(I); hold on for i = 1:size(BB,1) rectangle('Position',BB(i,:),'LineWidth',5,'LineStyle','-','EdgeColor','r');

end title('Face Detection'); hold off;

It s the second part.It need to be figured into the same image.That red rectangle need to be pixeld. I hope that someone should help me to solve this issue. Thank you very much.