CapnBloodbeard
RefChat Addict
Well, playing devil's advocate here.You've kind of answered your own question. If the player is blocking line of sight, they are interfering with an opponent. And therefore, committing an offside offence.
Key words here are "must be penalised"
In that image, the keeper's has no vision of the kicker - so he has no chance of knowing when the ball is kicked or where it's going.
That's a bit different to the keeper's view being blocked of the ball for a split second while the ball is in midair.
Just an observation on that image worth considering
I think this is a good discussion - the ins and outs of this aspect of law don't get discussed a lot