If it is only in your mind then I would say no, they cannot see it. But just because all images are in the mind of the experiencer that does not mean that they cannot also be in other minds as well. Similar inputs may produce similar (can't ever really say if they are identical) images in the mind of different viewers. However, someone who sees a ghost may have a mind that is sensitive to inputs that another mind is not (or chooses not to be), hence the first mind creates a ghost within itself with that input while the second does not create a ghost within itself. Some minds may by choice be bound more tightly within time and space, while others may keep themselves more open and transcendent.