A detector for detecting a birefringent object near a skin surface of a human body part or an animal body part includes a source for emitting optical radiation having first and second wavelengths and an incident polarization state. An imaging unit is configured to image the birefringent object near the surface includes a detection unit for detecting optical radiation scattered and/or reflected by the birefringent object and/or the surface at the first and second wavelengths. A control unit is configured to process a signal from the detection unit for discrimination between the birefringent object and the surface. The detection unit is configured to detect scattered and/or reflected optical radiation coming from the birefringent object and/or the surface, having a first polarization state corresponding to the incident polarization state and a second polarization state being different from the first polarization state.