Look for a steed with the aid of its picture

Bo Le was a famous master of horse-judging. He wrote a book titled Xiang Ma Jing (classics of how to judge a horse) to explain how to recognize a good horse. "A good horse has a wide forehead, bulging eyes and round hoofs," he wrote.

伯乐是一位著名的相马师，他写了一本叫《相马经》的书来教别人区分马的好坏。书上写着：良马有高高的额头，鼓起的眼睛，马蹄是圆圆的。

One day, according to a tale in the book, the son of Bo Le went out to look for a good horse. After a while, he came back, bringing with him a toad. He told his father, "I have found a horse similar that fits your description but its eyes are not bulging enough and hoofs not round." Bo Le did not know whether to laugh or to cry at this. He teased his son, "This horse is good at jumping rather than being ridden. What you have found matches my description, but it's not a good horse"

一天，他的儿子按着《相马经》上写的出去找好马。过了一会儿，他拿着一只癞蛤蟆回来了，对他的父亲说：“我找到了一匹马，大致跟你书上的一个模样，只是眼睛鼓得不够，蹄子也不是圆圆的。” 伯乐哭笑不得，开玩笑地说：“这匹马喜欢跳，但是不能骑啊。你这是照着图画找马。”

From what Bo Le said we draw the idiom, depicting those who work mechanically or try to locate something by following a description.

这个成语就来自伯乐的话，指机械地按着教条办事。