Some images get lots of views just because they need to be clicked on to be able to see the image properly and some get very few as they may be simple image that can be seen perfectly well in the thumb nail. In the case of the simple image I would expect a much higher percentage of sale/view ratio than I would a more detailed image. Some sites have a roll over magnification meaning that you don't need to click on an image to see it properly, others don't. In other words there is no real answer to your question.