When you add a new slide, you see "Set featured image". It seems to me like it would be clearer if this read "Set Slide Image".
I understood only after watching your video that you are using in fact the featured image of posts within wordpress, hence this may not be possible for you to change.
However, in the banner of the box, you have "Slide Image (940x200)". I gather 940x200 is the maximum size.
When I first saw "Featured Image", I wondered what that was about. I said to myself Featured image? I don't think I want to set a featured image, I just want THE image! So hmm, I have another suggestion to try and make this more obvious: "Slide Image (always the Featured Image of this post) (max 940x200)". This should make it totally clear what's going on.
Anyway, it's not bad what you have, I'm just trying to think of a way to make it even clearer.