1. A digital circuit for object identification in an image or a sequence of images, each image comprising an array of pixels, the circuit comprising: a processor comprising a plurality of processing components; a plurality of substantially synchronously-operating pixel processing elements, one for each pixel in the pixel array of an image, each pixel processing element comprising a pixel value register receiving a value for that pixel and a neighbor value register, wherein each pixel processing element is associated with at least one of the processing components, and wherein the processor is configured to cause the digital circuit to perform the following operations for respective pixels: receive adjacent pixel values and adjacent neighbor values for at least two adjacent pixels in the image or in either of the images respectively preceding and succeeding the image in the sequence of images, and in a series of iterations, replace the value in the neighbor value register with a function of: a current value in the neighbor value register; the adjacent pixel value from an adjacent pixel whose pixel value is different from the current value of the pixel value register; or the adjacent neighbor value from an adjacent pixel whose pixel value is the same as the current value of the pixel value register.