Various embodiments provide an image pre-processing method to accelerate image computing tasks. For example, an image is obtained from a camera of a portable computing device. Salient features of the image are identified by a number of techniques, such as identifying feature points, identifying gradients within the image, and other techniques and methods discussed herein. Based at least in part on the identified salient features, a saliency map of the image is computed. The saliency map includes a saliency value for each of at least a portion of the plurality of pixels. In this example pixels above a threshold saliency value are processed with an optical character recognition engine.