Original: If a complete sentence occurs in a caption, that sentence and any sentence fragments in that caption should end with a period.
Simplified: Any caption should start with a capital letter. If the caption is a complete sentence, it should always end in a period (or other appropriate punctuation). If the caption is not a complete sentence, it should not have a period at the end. When using complete sentences, put a period at the end of each sentence: This is a complete sentence. This is also a complete sentence. When using sentence fragments, do not put a period at the end: Part of a sentence Also a sentence fragment The rules for bulleted lists are the the same for numbered lists.