1. how can an impression be classified as circumstantial evidence, class evidence, and non-circumstantial
(individual) evidence?

Impression as circumstantial evidence, class evidence, and non-circumstantial  (individual) evidence:

An impression collected from the crime scene can be analysed by the forensic expert and then the result of the analysis will be handed over the investigation officer. Where the officer will study the nature of crime and will come to a conclusion about how the impression can be classified.

The officer will classify the impression as individual evidence when it posses the individual characteristics.  The evidence that has the class characteristics will be classified under class evidence. And then the circumstantial evidence which is grouping of evidence according to the crime scene. So, investigator will classify the impression according to the characteristics of the evidence.