1. A method to identify regions in images, the method comprising: receiving an image of a scene of real world; with one or more processors, computing an attribute based on pixel intensities in the image; with the one or more processors, using the attribute with a lookup table or a predetermined test, to identify at least one input to be used in processing the image to identify at least one maximally stable extremal region therein; wherein the at least one input is one of (A) a parameter Δ or Max Variation or both obtained by use of at least said attribute from the lookup table and used in said processing or (B) a portion of the image obtained prior to said processing by applying the predetermined test to a subsampled region in the image, the portion to be subject to said processing, or both (A) and (B); with the one or more processors, performing said processing to identify said at least one maximally stable extremal region based on said at least one input; wherein said processing comprises at least comparing a difference in intensities of a pair of pixels in the image to a predetermined limit, adding to a list, a pair of coordinates of a pixel in said pair of pixels, in response to finding said predetermined limit is exceeded, and repeating said comparing and said adding; and with the one or more processors, storing in one or more memories, the list as a representation of the at least one maximally stable extremal region identified by said processing.