A computer-implemented method configured for analysing images of hair and skin on a body of a subject, the method comprising: (i) receiving one or more images of a body part of the subject, the one or more images comprising a skin region corresponding to skin on the body part and a hair region corresponding to hair on the body part; (ii) processing the one or more images to determine diffuse reflectance of the skin region at different wavelengths of light; (iii) processing the one or more images to determine diffuse reflectance of the hair region at different wavelengths of light; (iv) determining a first contrast measure for a first pair of values of first and second wavelengths, wherein the first contrast measure is determined from (a) a difference between the diffuse reflectance intensity for the skin region in the first spectral band and the diffuse reflectance intensity for the skin region in the second spectral band, and (b) a difference between the diffuse reflectance intensity for the hair region in the first spectral band and the diffuse reflectance intensity for the hair region in the second spectral band, wherein the first and second spectral bands are respectively centred on the value of the first wavelength and the value of the second wavelength in the first pair of values; (v) repeating step (iv) to determine one or more further contrast measures for respective further pairs of values of the first and second wavelengths; and (vi) selecting first and second spectral bands corresponding to the pair of values of the first and second wavelengths that provides a contrast measure that meets a criterion; wherein each value of the first wavelength is in the range between 425nm and 650nm, and each value of the second wavelength is in the range between 600nm and 850nm, wherein in a pair of values, the value of the first wavelength is different to the value of the second wavelength. (i) receiving one or more images of a body part of the subject, the one or more images comprising a skin region corresponding to skin on the body part and a hair region corresponding to hair on the body part; (ii) processing the one or more images to determine diffuse reflectance of the skin region at different wavelengths of light; (iii) processing the one or more images to determine diffuse reflectance of the hair region at different wavelengths of light; (iv) determining a first contrast measure for a first pair of values of first and second wavelengths, wherein the first contrast measure is determined from (a) a difference between the diffuse reflectance intensity for the skin region in the first spectral band and the diffuse reflectance intensity for the skin region in the second spectral band, and (b) a difference between the diffuse reflectance intensity for the hair region in the first spectral band and the diffuse reflectance intensity for the hair region in the second spectral band, wherein the first and second spectral bands are respectively centred on the value of the first wavelength and the value of the second wavelength in the first pair of values; (v) repeating step (iv) to determine one or more further contrast measures for respective further pairs of values of the first and second wavelengths; and (vi) selecting first and second spectral bands corresponding to the pair of values of the first and second wavelengths that provides a contrast measure that meets a criterion;