Hiding in the brush, the leopard was not seen by the hunters.

this sentence contains a

participle, incorrectly punctuated
participle, correctly punctuated
a dangling participle
gerund, not a participle

This sentence contains a participle, correctly punctuated.
The phrase hiding in the brush is the participle in this sentence (and it tells us what the leopard was doing), and it is correctly punctuated - there has to be a comma after this phrase because it is found in the beginning of the sentence, before the subject the leopard.