Here you can see for instance a copy by Maruyama Oukyo (on the right from a printed catalogue) of the Guan Yu painting by the early 15th century master Minchou (on the left).
In the inscription he is declaring it as lin 臨, a Chinese term meaning exact copy after the original. It is not so exact at all. It seems the 18th century Japanese does not want to face the god of war any more directly.
Oukyo's copy of Minchou's Guan Yu is a great painting too. It also is executed in his personal brush work.
Another form of a study copy would be fang 倣, meaning in the manner of. Used mainly by amateurs it is often not at all in the manner of. This rather should be taken as some intellectual attachment to the reported traditions.