auto crop length of hand

hi. im doing a project to build an automatic system to detect length of hand from elbow to fingertips. first i read the image>filter>subtract background using k cluster. now i need to crop the image to get the hand length . the problem is if i crop the hand, it is not automatic system. how can i get the length of hand automatically? below is the coding #handcrop | | |

clear all
clc
A=imread('img1.jpg');
h=ones(5,5)/25;
A2=imfilter(A,h);
imshow(A2), title('H&E image');
text(size(A2,2),size(A2,1)+15,...
     'Image courtesy of Alan Partin, Johns Hopkins University', ...
     'FontSize',7,'HorizontalAlignment','right');
 lab_A2= rgb2lab(A2);
 ab = lab_A2(:,:,2:3);
nrows = size(ab,1);
ncols = size(ab,2);
ab = reshape(ab,nrows*ncols,2);

nColors = 3;
% repeat the clustering 3 times to avoid local minima
[cluster_idx, cluster_center] = kmeans(ab,nColors,'distance','sqEuclidean', ...
                                      'Replicates',3);
pixel_labels = reshape(cluster_idx,nrows,ncols);
imshow(pixel_labels,[]), title('image labeled by cluster index');
segmented_images = cell(1,3);
rgb_label = repmat(pixel_labels,[1 1 3]);

for k = 1:nColors
    color = A2;
    color(rgb_label ~= k) = 0;
    segmented_images{k} = color;
end

imshow(segmented_images{1}), title('objects in cluster 1');
imshow(segmented_images{2}), title('objects in cluster 2');
imshow(segmented_images{3}), title('objects in cluster 3');
mean_cluster_value = mean(cluster_center,2);
[tmp, idx] = sort(mean_cluster_value);
blue_cluster_num = idx(1);

L = lab_A2(:,:,1);
blue_idx = find(pixel_labels == blue_cluster_num);
L_blue = L(blue_idx);
is_light_blue = imbinarize(rescale(L_blue));
nuclei_labels = repmat(uint8(0),[nrows ncols]);
nuclei_labels(blue_idx(is_light_blue==false)) = 1;
nuclei_labels = repmat(nuclei_labels,[1 1 3]);
blue_nuclei = A2;
blue_nuclei(nuclei_labels ~= 0) = 1;
imshow(blue_nuclei), title('blue nuclei');|||

[jue xi]

this is the result after run the coding

[jue xi]

i need to get at least like this to crop the hand,