Regarding the slide-bg-light.jpg it’s only a simple image for background.
At really the image it’s not going to cover up in mobile. On mobile the Desktop and Laptop devices are being intentionally hide with the classes tp-caption tp-resizeme d-none d-sm-block. This is because on mobile we don’t have enough space to show the images.
Regarding: “And in the other hand: It’s really necessary create an image width 1920 pixels?”
No. It’s not required a image with 1920px if wants to. You can use a small image.
Regarding locate the images of index-corporate-8, you mean the real images ? The images used in our preview ?
The images we use in our preview are from Shutterstock (premium). Unfortunately we don’t have the link of exact images we used on the demo. But the Shutterstock has a great search system where you can do a search with image upload (you can get the image from our preview), so will return images like in the preview.
Another very good bank of images (free) is https://unsplash.com. We also use some images from this source.