A control apparatus for effecting a control action in respect of a security level controlled function within a virtual or mixed reality system, said control action corresponding to a predefined bodily movement of an authorised user of said function, wherein the authorised user of said function is defined by a predetermined criterion in respect of a selected body part, the control apparatus comprising: - a detection module for detecting the predefined bodily movement made by an unverified user to effect the control action in respect of said function of said virtual or mixed reality system; - a multi-spectral imaging system for capturing spectral reflectance and/or emission data at a plurality of wavelengths in respect of said selected body part of said unverified user; - an analysis module for analysing the spectral reflectance and/or emission data of the unverified user; and - a storage module having stored therein stored data representative of one or more spectra corresponding to respective one or more authorised users' body part(s) registered in respect of said virtual or mixed reality system, - wherein said analysis module includes a matching module for, in response to detection of the predefined bodily movement of the unverified user, receiving data representative of a spectrum derived from the spectral reflectance and/or emission data captured by said multi-spectral imaging system in respect of said unverified user's selected body part, comparing at least a portion of said received data with said stored data to determine a match with that of one of the one or more registered authorised users of said function in respect of which said bodily movement has been detected, and wherein said analysis module is configured to output a signal to effect said control action in respect of said function only if a match is determined. - a detection module for detecting the predefined bodily movement made by an unverified user to effect the control action in respect of said function of said virtual or mixed reality system; - a multi-spectral imaging system for capturing spectral reflectance and/or emission data at a plurality of wavelengths in respect of said selected body part of said unverified user; - an analysis module for analysing the spectral reflectance and/or emission data of the unverified user; and - a storage module having stored therein stored data representative of one or more spectra corresponding to respective one or more authorised users' body part(s) registered in respect of said virtual or mixed reality system, - wherein said analysis module includes a matching module for, in response to detection of the predefined bodily movement of the unverified user, receiving data representative of a spectrum derived from the spectral reflectance and/or emission data captured by said multi-spectral imaging system in respect of said unverified user's selected body part, comparing at least a portion of said received data with said stored data to determine a match with that of one of the one or more registered authorised users of said function in respect of which said bodily movement has been detected, and wherein said analysis module is configured to output a signal to effect said control action in respect of said function only if a match is determined.