Extract and Edge and Calculate its lenght

Dear all ;

i have an image i found the edge and i need to calcuate it lentgh , what is the best way for that

my code as follow but i feel it is not correct.

clc; clear; a = imread('st-2.jpg'); b=rgb2gray(a); BW1=im2bw(b);

        figure (1), imshow(BW1)
        BW2=edge(BW1,'canny');
        BW21 = bwmorph(BW2,'remove');
        figure  (2), imshow(BW21)
           [L,NUM] = bwlabel(BW21,8);
       [m,c] = find(L == 1);
         S = regionprops(L,'Area');
         r=struct2array(S);
         [l,w]=size(b);

[Image Analyst]

You forgot to attach st-2.jpg. Generally jpg iamges are not good for image analysis. And explain what you mean by the length. Do you mean just the sum of all white pixels in the edge image? Or of just one of the blobs? Or something else?

[Md Mahbub Hossain]

Is there any reason that .jpg image is not good for image processing?

[KALYAN ACHARJYA]

Please answer the question raised by @ImageAnalyst sir

Length means?