Stop what you're doing, go to this post at BiblioOdyssey, and follow the instructions.

In the Edo period, people believed that kappa were real, and there were even specialist books about them. The most well-known of these was An Overview of Kappalogy (『水虎考略』), compiled by KOGA Touan (古賀侗庵) in 1820. The work shown here, Guide to [the?] 12 Types of Kappa (『水虎十二品之図』), is a collection of twelve images copied from the Overview with some extra details added. The Guide was authored by SAKAMOTO Kouen (坂本浩然), a court physician in Kii Province, and his younger brother SAKAMOTO Juntaku (坂本純沢), a court physician in Takatsuki, Settsu.

(I should probably note that I am lazily translating suiko (水虎, literally "water tiger") as kappa because although I can find webpages that allege a difference between the two terms, they certainly seem to be used synonymously here.)