There are some special circumstances where the position of a virtual image can be measured.
Assume you have a real object located, say, 2 meters in front of a plane mirror. The virtual image is located 2 meters on the other side of the mirror. Of course, no light from the object actually goes there.
However, let's further assume that the mirror is a partially reflecting one; a typical interrogation room with observation room setup. The object and we, are in the observation room, and the virtual image, is in the interrogation room, even though the rays of light responsible for the virtual image never enter the interrogation room. Now, some of the light from the object does penetrate the mirror, but we need to ignore it; it never comes back, nor does it forms any type of image for us. (But note the use below!).
But we, in the observation room, will simultaneously see the real objects in the interrogation room, and the virtual image in the same room. The two will be superimposed in three dimensional space.
A friend in the interrogation room can help us. He could hold up an extended tape measure and we could use parallax (moving our head back and forth) to determine what point on the real tape measure coincides with the virtual image.
Our friend could help us in another way. With the right lighting, he will be able to see the real object in the observation room (Remember those rays from above?). He will also see a virtual image of himself, and of his tape measure, in the observation room, courtesy of his side of the partially reflecting surface. He will be able to do the same parallax tests and confirm our determination of where on the virtual tape measure image the real object is located...