A method of determining a hierarchy of estimated motion between a pair of image frames of a given scene comprising: a) calculating respective integral images for each of said image frames; b) selecting at least one pair of corresponding regions of interest within each frame; c) for each pair of corresponding regions of interest: i. calculating an integral image profile from each integral image, each profile comprising an array of elements, each element comprising a sum of pixel intensities from a swath of said region of interest for said frame, said calculating an integral image profile comprising sub-sampling said integral image at a first sub-sampling interval at a first selected level of said hierarchy and for each repetition of step c), sub-sampling said integral image at successively smaller sub-sampling intervals; ii. correlating said integral image profiles for said pair of corresponding regions of interest to determine a relative displacement of said region of interest between said pair of frames; iii. dividing each region of interest into a plurality of further regions of interest to go to the next level of the hierarchy, said dividing being responsive to said correlating determining more than one displacement within said region of interest for determining a non-uniform division (H1, H2, V1) of said region of interest and for dividing said region of interest differently according to said non-uniform division; and repeating step c) for said further regions of interest until a required hierarchy of estimated motion for successively divided regions of interest is provided. a) calculating respective integral images for each of said image frames; b) selecting at least one pair of corresponding regions of interest within each frame; c) for each pair of corresponding regions of interest: i. calculating an integral image profile from each integral image, each profile comprising an array of elements, each element comprising a sum of pixel intensities from a swath of said region of interest for said frame, said calculating an integral image profile comprising sub-sampling said integral image at a first sub-sampling interval at a first selected level of said hierarchy and for each repetition of step c), sub-sampling said integral image at successively smaller sub-sampling intervals; ii. correlating said integral image profiles for said pair of corresponding regions of interest to determine a relative displacement of said region of interest between said pair of frames; iii. dividing each region of interest into a plurality of further regions of interest to go to the next level of the hierarchy, said dividing being responsive to said correlating determining more than one displacement within said region of interest for determining a non-uniform division (H1, H2, V1) of said region of interest and for dividing said region of interest differently according to said non-uniform division; and i. calculating an integral image profile from each integral image, each profile comprising an array of elements, each element comprising a sum of pixel intensities from a swath of said region of interest for said frame, said calculating an integral image profile comprising sub-sampling said integral image at a first sub-sampling interval at a first selected level of said hierarchy and for each repetition of step c), sub-sampling said integral image at successively smaller sub-sampling intervals; ii. correlating said integral image profiles for said pair of corresponding regions of interest to determine a relative displacement of said region of interest between said pair of frames; iii. dividing each region of interest into a plurality of further regions of interest to go to the next level of the hierarchy, said dividing being responsive to said correlating determining more than one displacement within said region of interest for determining a non-uniform division (H1, H2, V1) of said region of interest and for dividing said region of interest differently according to said non-uniform division; and