1. A method of computer-aided detection, comprising: (i) receiving an input set of training images of a target structure; (ii) spatially realigning the input set of training images to different landmarks to generate multiple bags of training images, wherein at least one of the multiple bags comprises substantially all the training images in the input set realigned to at least one of the different landmarks; (iii) training a spatial ensemble of detectors using the multiple bags of training images; and (iv) generating an output result by using the trained spatial ensemble of detectors to automatically detect the target structure in an input image.