This game has no Steam overlay support, therefore players can't just F12 to take screenshots and upload. Here are the steps to deal with this issue:

Download SteaScree [steascree.download] and install.

Game ID: 620080

Take a screenshot of your game using printscreen or other screenshot tools -> Add screenshots to queue -> Copy screenshots to game directory -> Prepare screenshots for uploading.

You should be able to see the screenshots on the game's page in your library after restarting steam.