System and method for assessing the occurrence of an unknown substance in a sample that comprises multiple entities. A reference library is provided comprising a plurality of reference data sets representative of at least one known substance. A first feature of the entities is assessed wherein the first feature is characteristic of the unknown substance. A region of interest is selected wherein the region of interest comprises at least one entity exhibiting the first feature. A spatially accurate wavelength resolved Raman image is obtained wherein each pixel in the image is the Raman spectrum of the sample at the corresponding location. The spatially accurate wavelength resolved image is assessed to thereby identify the unknown substance.