1. A skin marker for providing a reference point for a plurality of different medical imaging procedures, said marker comprising: at least one substance having one or more properties chosen from (i) radiance, (ii) hydration, (iii) radiopaqueness, (iv) radio luminescence, and (v) radioactivity for detection by one or more of (i) X-ray, (ii) Computer Tomography (CT), (iii) MRI, (iv) Ultrasonic scanning processes, and (v) Positron Emission Tomography (PET); and at least one marking that is recognisable by an optical electronic imaging process.