What is a controlled mosaic?

Images are scanned from aerial photographs or acquired using a digital camera and then mosaicked together using image processing software like ERDAS Imagine or Photoshop. Using an orthophoto or a map, such as a USGS Quad map, the mosaicked images are "rubber-sheeted" using known control points or easily identified locations to geo-reference points in the mosaic. Though a controlled digital mosaic is "fitted" to a map of known accuracy, there is no rigorous mathematical rectification for relief displacement.