Put the images in front of your eyes.

Bring your finger between your face and the image at almost middle of the distance.

Now look at your finger.

Move your finger back and forth and notice the background (where your picture is)

While doing this, notice that at a particular distance, the images in background will perfectly overlap each other.

That's your moment.

Pull out your finger and look at that image.

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It worked on everyone I have tried to teach. You may always need help of your finger or a tip of a pencil or whatever. But it's lot easier to get those images to merge this way.