You can use screenshots, regardless of copyright and ownership, as long as its use falls under 'criticism and review'.
What that means is that using screenshots as an accompaniment to an article that in some way analyses the subject, you're fine.
So technically, screenshots of the AGS editor in a 'how to use AGS' article would be illegal. Screenshots of the editor in an article called 'why AGS is awesome' is fine.
What's more, you could use screenshots in a plain 'how to use AGS' article as long as the article contains even the teeniest element of criticism & review. So if it started with "I love AGS, here's how it works..." you're technically fine to use copyrighted images without the permission of the owner, links, expression of copyright ownership etc etc.