I need to figure out when a ped is not visible to the human player on their screen. I'm not talking about whether the player's ped has a line of sight to the ped, I'm talking about are there any pixels being displayed at this moment which belong to the ped. 

I would've thought the Entity.IsVisible or Entity.IsOnScreen properties would've done the trick, but both always seem to return true. 

Is there any way to do this? 

Did you try the native IS_ENTITY_ON_SCREEN? From the nativeDB: "Returns true if the entity is in between the minimum and maximum values for the 2d screen coords. 
Still returns true even if the entity can't be seen yet is between the appropriate 2d screen coords (like above)." So it looks like it only detects if it is out of screen horizontally.

If that doesn't work you could use World.ConvertWorldPositionToScreenPosition() and check if it is inside the resolution rectangle, I haven't tried it but I think it should work.

14 hours ago, alexguirre said:

If that doesn't work you could use World.ConvertWorldPositionToScreenPosition() and check if it is inside the resolution rectangle, I haven't tried it but I think it should work.

This seems to be working. Thanks.