The "curve" of an image relates to how the spectrum changes from white to black. A digital image has a straight line. An analog image (film) has more of an "S" curve. If you want an image to have more "life" or "reality" to it, you can play with this curve in photo editing software, like GIMP.

The reality is that an analog "S" curve is going to have a higher contrast because the line from black to white is steeper.



This is a digital image that I made look more like an analog image.