In English this is written a 'sound and image'. It is a set phrase like salt and pepper.
Yes, that is very good and has been added to the incubator. Thank you very much.
No, not always. It would be the title of an event. In this case we don't speak about the image and the sound, but generally about these concepts. The article is a demonstrative actually, and this is the origin of artcles in many languages, including the Romance ones, since Latin has no articles, instead Ancient Greek did.