how to scramble pixels of specific part of image

Can anyone suggest a way to scramble all the pixels within a circle of an image?

I am using this code to scramble all the pixels within an image:

img=imread(SpecificStimuli);
rmig=reshape(img,[],size(img,3));
n=size(rmig,1);
simg=rmig(randperm(n),:);
simg=reshape(simg,size(img));
imwrite(simg, OutputName);

But, rather than scrambling all the pixels I would like to only scramble the pixels within this oval of the original image:

Radius=608; Centered at: Center Row=676 Center Column=642

Answer 1

[DGM]

Consider the example:

% an image
inpict = imread('peppers.png');

% generate a mask using any appropriate method
% see also imellipse(), drawellipse()
sz = size(inpict,1:3);
points = makeoval(75,[180 250],-135); % attached
mask = poly2mask(points(:,1),points(:,2),sz(1),sz(2));
mask = repmat(mask,[1 1 sz(3)]); % expand the mask

% get the masked pixels as a Mx3 color table, shuffle it
extractedCT = reshape(inpict(mask),[],sz(3));
extractedCT = extractedCT(randperm(size(extractedCT,1)),:);

% compose the output image
outpict = inpict;
outpict(mask) = extractedCT;

% show it
imshow(outpict)

Might want to be specific when you say "oval'. Someone might guess that you mean "strictly an ellipse", but I don't think many people would think you actually meant "circle".