While we didn't have front seats, I had learned that I could go up to the front of the bus and park on the top step, thus not blocking anyone's view and get my photos out the front window.   They were not as strict as here about getting in front of the 'white line'.   We had also learned that Southern South America has not evolved to the point of being as litigious as the United States thus, they were more lenient on what people could do!