title: How to "zero" everything within a masked part of an image in OpenCV
body: <p>If I have an image (IplImage 8-bit) and a binary mask (which is also an 8-bit IplImage of the same size, where every pixel has a value of either 0 or 255), how can I make every pixel in the image that corresponds with a pixel in the mask with a value of zero have a value of zero, and every pixel in the image that corresponds with a pixel in the mask with any other value (namely 255) have the same value as in the original image?</p>
  
  <p>In other words, anything that is "in the mask area" will keep its original value, and anything outside the mask area will become zero.</p>