As reported by Kotaku, Steam is going to removed non-screenshot content from the slideshow on the store pages of sold products. This will include pre-rendered images, artwork, images listing rewards, and anything else that is not a screenshot.
The story first emerged on Facepunch forums, where one of the users made a screenshot of a notification sent by Valve. As the missive itself puts it:
“We haven’t been super crisp on guidelines for screenshots in the past, so we’d like to take this opportunity to clarify some rules in this space. When the ‘screenshot’ section of a store page is used for images other than screenshots that depict the game, it can make it harder for customers to understand what the product is that they are looking at. Additionally, we’re going to start showing game screenshots in more places as described above, and these images need to be able to represent the game.”
Valve themselves have applied this rule to their DotA 2 page, which previously contained mostly artwork for the game.
All of this is said to be a part of an upcoming essential update of Steam, which, among other features, is rumored to design the Home Page, put more focus on the activity of your Steam friends, and offer more options to the Curators.