1. A machine-implemented method performed on a portable processing device including an image-capturing component, the machine-implemented method comprising: capturing a first image frame via the image-capturing component, the captured first image frame having a plurality of regions, each of the plurality of regions having a subset comprising a block of pixels; capturing a second image frame via the image-capturing component, the captured second image having a plurality of regions; adaptively searching for a matching block of pixels in each of the plurality of regions of the captured second image frame with respect to a corresponding one of the block of pixels in respective ones of the plurality of regions of the captured first image frame; and estimating a motion vector with respect to each of the plurality of regions of the captured second image frame based on positions of the matching blocks of pixels with respect to positions of the blocks of pixels in the respective ones of the plurality of regions of the first image frame.