1. A method comprising: using a display controller to: (a) specify at least two sites in a frame, the sites being arranged in a particular spatial distribution, each site corresponding with the pixel locations of a block of pixels, each block having at least two pixels; (b) calculate a block parameter for each block of first and second frames in a sequence of frames, each block parameter being calculated from the pixels of a respective one of the blocks; (c) generate a block-pair similarity determination for each pair of spatially-corresponding pixel blocks of the first and second frames by determining whether there is a difference between the respective block parameters which is greater than a particular block-level threshold; and (d) generate a frame similarity determination by combining the block-pair similarity determinations to detect a camera shake when the first and second frames are not similar and to indicate a shake-free image is not probable, and to indicate a shake-free image is probable when the first and second frames are similar.