On some cases where exam results are manipulated
There is no counterneasure which is bulletproof and administratively feasible. If I want to cheat as a teacher, I will always find ways around such a system. 

The only way would be to have the exam taken by independent administrative staff, they scan all answers as proof, and then hand it to the teacher. 
Online results could be watermarked (e.g. by an MD5 / SHA hash), but I don't know if such systems exist. 

If I really want to upgrade or downgrade a student, I would not take the risk of manipulating the exam, but to adjust my measures for deciding what is true and what is false and to which account I'm willing to accept "a good idea which did not lead to the correct result". 

As a teacher, I like to have electronic submissions since they are a proof and students usually have nearly no means of changing them afterwards. But I prefer  doing the grading with paper and pencil.