I = imread ( 'saturn.png' );
imshow ( I );
I2 = I;
thick - 20;
I2(:,end+1-thick:end) = 255;
I2(:,1:thick) = 255;
I2(end+1-thick:end,:) = 255;
I2(1:thick,:) = 255;
imshow ( I2 );
imwrite ( I2, 'saturn.jpg' );