Set the comparison up correctly
Compare plants from the same batch and at similar stages under similar lighting. Capture the whole plant and close-up details. Note whether marks appear on one leaf or across several plants.
Know the limits of photos
A photo captures one moment and angle. For a meaningful comparison, ask for the date, batch identifier and several views. Query identical images used for different batches.
Write a usable observation record
Record the number of plants inspected, parts affected and visible signs. Mark roots as not assessed if they could not be seen. A later reader can then distinguish observations from missing information.