How to use images in my templates?

I am a new user here at Envato market and I want to sell html+css templates.
To add photos in my templates I can use the entire PhotoDune? for example this image
just add it with this watermark?

Where I need to put the backlink to the author’s photo page?

As far as I know, you can use it but you may need to include the image URL to your credit page

What is a credit page?

It’s the place where you include credits (links) to the original authors’ for the items you have used.
You can use the documentation or on the item page, you can include the resources