1. An image processing method performed by one or more hardware processors of a computing device, the method comprising: repeatedly imaging, using a camera, a scene to form a series of input image; for each of at least a first subset of the input images, conducting a colour calibration procedure of: populating a foreground colour histogram, stored in a memory, with data values representing the frequency of occurrence of colour values in a stencil area of the input image of the first subset; populating a background colour histogram, stored in the memory, with data values representing the frequency of occurrence of colour values outside of the stencil portion of the input image of the first subset; and updating the stencil area based on a determination, from the colour values of pixels in the input image, of likelihood values representing probability that pixels belong to an image area of interest, the likelihood value for each colour value being determined from a combination of the stored foreground and background colour histograms; and for each of at least a second subset of the input images, conducting a colour replacement procedure of: generating a depth map of the scene corresponding to the input image of the second sub set; determining, from the depth map, the area of interest in the input image of the second subset to which colour replacement processing can be applied; identifying pixels within the area of interest of the input image having a colour value within a specified colour range; replacing the colour value of each identified pixel with a replacement colour value to generate an augmented output image; and outputting the augmented output image to a display.