Yes, it's a subject without a predicate. So it's not a complete sentence.
That doesn't mean it doesn't make sense. Let's say there's an image with the caption "A man looking at a fish in a tank." That's similarly a subject without a predicate, but it still makes sense as a photo caption.
That doesn't mean it doesn't make sense. Let's say there's an image with the caption "A man looking at a fish in a tank." That's similarly a subject without a predicate, but it still makes sense as a photo caption.