I got boundary box how can 1 crop only the boundary box automatically and display as a image

This is my code I= rgb2gray(imread('oct_485.jpg'));

mask =I > 10; % Mask is bright stuff. figure,imshow(mask);

st = regionprops(mask, 'BoundingBox', 'Area' ); [maxArea, indexOfMax] = max([st.Area]);

rectangle('Position',[st(indexOfMax).BoundingBox(1),st(indexOfMax).BoundingBox(2),st(indexOfMax).BoundingBox(3),st(indexOfMax).BoundingBox(4)], 'EdgeColor','r','LineWidth',2 );