What is an Audiovisual artifact?
An audiovisual artifact is a picture or sound clip from the game. It needs to be something concrete, such as a screenshot or sound clip, and not something from the memory of the user.
Why does an Audiovisual artifact grant an exception to the Game Identification ban?
One of the primary reasons for the Identify This Game (ITG) ban was that we can't rely on the memory of our users. Users remember details incorrectly, and because of this we can't guarantee the information they list is correct, and are unable to reliably answer their question.
There is also the fact that even if all the details listed are correct they could still match any number of games, and not just one game. Due to this there is no way for a user to provide a definite answer to the question without first getting confirmation from the asker.
An audiovisual artifact faces neither of these problems. A screenshot of a game faces no issues of users remembering things incorrectly, since it's not from memory. So the memory problem no long exists. The same applies to a sound clip from the game.
A screenshot also can only come from one game, so the issue of a screenshot matching multiple games also doesn't apply. Once again, the same thing applies to sound clips.
Why can't pictures or songs made from memory be used?
A picture or song made from memory by a user faces the same problem that a user typing out a textual description of things they remember from the game. That is, we can't trust their memory. It was very common for users to list details about a game and get some of those details wrong. Converting those details into a picture or a song doesn't change really change that. Pictures and songs from memory can still be remembered incorrectly by the user.
The issue of a description being able to match multiple games is as true of pictures and sounds made by the user as it is for textual description. Unless a user is able to create a perfect recreation of a picture of song from a game it's possible for it to match more games than the one the asker is thinking of, which means no user can definitely answer the question. Since there's no way to know if a recreation is perfect, we are unable to say that the question can be reliably answered.