This is a truly wonderful old icon, but a controversial one. In Zo Zayong's 1984 book Korean Tiger, under the photo of it on page 29 it is labeled "Mountain Spirit, mineral color, silk base, 173cm x 90cm, 18th Century" -- and no other information is given. It was assumed to be a San-shin [mountain-spirit] painting because of the presence of a tiger, being amusingly fed or given a drink from a bottle by a dongja child-attendant. This does follow the general rule of Korean folk religious paintings, that if there is a prominent tiger together with a royal-looking elder-human figure (and a pine tree, in almost every case), then it is indeed a Sanshin. But looking closely at this one, I now believe that it is actually a Dok-seong [Lonely Saint] icon, just with some Koreanized blending of motifs.
This tiger is a good deal smaller (seeming like a cub) than the usual ones in Sanshin paintings, which are always full-sized and mature tigers. This one seems to be there just for the mockingly-comic Korean-folk-motif effect. Moreover, the main figure here has a bald head with no headgear such as a top-knot cover, Daoist cloud-cap or crown (possible for Sanshin but unusual), and a monastic tonsure-circle on top. He features the pointed version of the long- eyebrow motif always used for the Dokseong (which is derived from the Arhat Pindola) -- fairly often used for Sanshin as a motif conflation, yes. His robe is, however, not the typical embroidered king's-style robe but rather an open-front chest-exposing Buddhist-style one, undecorated save for the gold lining around its edges. He holds nothing in his hands and has one bare foot up in crossed position, which is a Buddhist style (Sanshin almost always wears official boots). The attendant behind him holds a Seon [Zen, Meditation] Master's fly-whisk, very Buddhist and sometimes seen in Sanshin paintings. There is an elaborate golden incense burner on the rock Just beside the main figure, a Buddhist feature that is seen in Sanshin paintings only in rare cases. The rest of the features in the beautifully elaborate background, mainly Daoist symbols of long life, are common in both Sanshin and Dokseong icons.
There are many cases of Sanshin paintings that contain Buddhist motif-symbols within them, sometimes directly taken from the Dokseong traditions, as detailed in my book Spirit of the Mountains. However, here the Buddhist Dokseong elements dominate and the Sanshin elements are distinctly weaker. Altogether then, I'm going to disagree with my old teacher and judge that this is an opposite case -- a Dokseong that is very similar to a Sanshin, but just not enough to make the grade, to be considered a Sanshin. This case certainly demonstrates the conflation and mixing of motifs and elements, common in Korean religious folk paintings, that can make certain identifications very difficult to judge.