It's called "Featured Artwork Showcase" and it finally allows you to have a Full Screen picture on your profile
Besides it has a larger size and you don't have to trick steam with coding and bigger resolution images to have a nice looking profile. It looks like this

I am surprised that big pat of the community still haven't found out about this feature. And a lot of people still make separate prictures and there is always this "+some more artworks" section below
Don't be old and use Full Screen Showcase! It will be easier, won't cost you much time and will look much better, trust me!

This Guide is a small advice for people who like style and beauty ;)
I really hope more people will find this out with or without my help
Thanks and have a great day!