1if the reflected/refracted rays are diverging in nature, then they form a virtual image (since they do not actually meet) just appear to be coming from the place where the virtual image is formed...
try drawing some figures of diff cases urself or consult any example given in book...
they cant b taken on a screen bcz at the place where the image is formed, the reflected/refracted rays are not there....
we can see the image because our eye gets the rays from the object after being reflected and they form the image at the place from where the rays appear to be coming, i.e. from the back of the mirror/interface.... same in the case of any other optical instrument...