If you have only circle on the image like below
clc,clear
I = imread('img.png');
I1 = im2bw(I,graythresh(I)); % binarize image (0,1)
[row, col] = find(I1); % find white pixels (1 value)
ix = round( mean(col) ); % mean column
iy = round( mean(row) ); % mean row
imshow(I1)
hold on
plot(ix,iy,'or')
text(ix+10,iy+10,'CircleCenter')
hold off
