I = imread('IMG_4.jpg');
    J = imread('IMG_5.jpg');

    I = single(rgb2gray(I)); % Conversion to single is recommended
    J = single(rgb2gray(J)); % in the documentation

    [F1 ,D1] = vl_sift(I);
    [F2 ,D2] = vl_sift(J);

    % Where 1.5 = ratio between euclidean distance of NN2/NN1
    [matches, score] = vl_ubcmatch(D1,D2,1.5);

    subplot(1,2,1);
    imshow(uint8(I));
    hold on;
    plot(F1(1,matches(1,:)),F1(2,matches(1,:)),'b*');

    subplot(1,2,2);
    imshow(uint8(J));
    hold on;
    plot(F2(1,matches(2,:)),F2(2,matches(2,:)),'r*');