Draw circle in a image

Suppose i have an image. On that image i want to draw a circle which has specific radius and center. What function i need to use to draw a circle in a image?

[Walter Roberson]

http://matlabwiki.mathworks.com/MATLAB_FAQ

Answer 1

[David Sanchez]

imshow(your_image);
hold on
t=0:0.1:2*pi;
%x_o and y_o = center of circle
x = x_o + radio*sin(t);
y = y_o + radio*cos(t);
plot(x,y,'r');
hold off