From the Curator Guide:
An additional note regarding drawings: drawings are ok because, like photos, they can show visual evidence of the individual organism observed. If you don’t think the drawing was of the observed organism (e.g. it’s just a drawing of the species, not of an individual), talk to the observer and ask them to clarify what their drawing depicts… If you cannot identify the organism from the drawing, treat it like a blurry photo and vote that the community cannot improve the ID.