raspberry pi web cam server

I am doing operations as described here, but matlab can not read video .why? https://pimylifeup.com/raspberry-pi-webcam-server/

my code:

raspberry_web_server = 'http://192.168.1.23:8081//shot.jpg';

frames = 0;

red_t=0.18;

i=0;

while (frames <= 12)          

        data= imread(raspberry_web_server); 

        frames = frames + 1;    

        diff_im = imsubtract(veri(:,:,1), rgb2gray(data)); 

        diff_im = medfilt2(diff_im, [3 3]);       

        ...