You can make the following modification (make sure to place your cellfun calls after the for loop)
cropped_imgs = cellfun(@(I) imcrop(I, [133 133 150 150]),...
grayImages, 'UniformOutput', false);
However, are you using images and grayImage for anything other than getting the cropped grayscale images? If you don't need them then you don't store them. For example, the following would be much better:
N = 4;
croppedGrayImages = repmat({zeros(400,400,3)}, N, 1); % preallocate what you wish to store
for n = 1:N
I = imread(sprintf('car_%d.jpg',n)); % cars_%d as an example
resizedImage = imresize(I,[400,400]);
grayImage = rgb2gray(resizedImage);
croppedGrayImages{n} = imcrop(grayImage,[133 133 150 150]); % store output
end
note that space for croppedGrayImages is preallocated and resizedImage and grayImage initialise on the first loop.
