Cold sores are always on the face usually on the lips (you can have an outbreak of the same virus on the genitalia but those aren’t considered cold sores). Impetigo is usually in the same area, but can be found anywhere. Cold sores are a viral infection, impetigo bacterial.

I guess cold sores can look crusty esp later on, but they do have a more defined shape/ less area will be affected than impetigo.