Screenshots posted on Steam store pages must now be genuine in-game screenshots, according to new Valve guidelines.

In a message to Steamworks developers, Valve UI designer Alden Kroll wrote that "any images you upload to the 'screenshot' section of your store page should be screenshots that show your game."

"This means avoiding using concept art, pre-rendered cinematic stills, or images that contain awards, marketing copy, or written product descriptions," Kroll clarified.

"Please show customers what your game is actually like to play."

Valve itself has replaced many screenshots for its popular online game Dota 2, which previously had pieces of concept art listed as screenshots.

The changes come as part of an upcoming storewide refresh, which will see screenshots used in more places; in another policy amendment, Valve will now require that developers tag screenshots that contain mature content.

Misleading screenshots were a significant part of the controversy surrounding space sim No Man's Sky, whose screenshots depicted features and graphical capabilities that were missing in the shipped game.

The phenomenon is not even limited to that game, as doctored screenshots appear throughout the AAA industry and beyond.

Such screenshots "can make it harder for customers to understand what the product is that they are looking at," reads Valve's message.

The storefront alterations are expected to hit in the next few weeks.