1. A method for determining an intensity value of an interaction with a computer program, the method including: capturing an image of a capture zone; identifying a representation of an input object in the image; identifying an initial value of a parameter of the input object, the parameter identifying one or more of a shape, color, or brightness of the input object, the parameter being affected by human manipulation of the input object; capturing a second image of the capture zone; identifying a second value of the parameter of the input object; determining an extent of change in the parameter, the extent of change being the difference between the second value and the first value; and providing an activity input to the computer program, the activity input including an intensity value representing the extent of change of the parameter.