Hi jos bos.
The purpose of tactile imaging is to induce a feedback mechanism in the way you move energy- you move energy, and feel a tingle when you do. You don't just think you're moving energy, you feel it.
Using your physical fingers in the beginning of the exercise is only done in the beginning, to help you to target an area with your mind. You touch it, you take away the finger and feel the remaining feeling, and then using your mind, you keep the tingle going and expand it to other areas of the body. This is to teach you how energy feels as it moves, and to help you have an idea of when it's working and when it isn't.