Leakproof exam papers

So the widespread use of technology, in particular smartphones, seems to have opened up scope for rather more prevalent cheating in exams.

The early part of the exam preparation pathway is presumably still fairly secure. However, when the examination papers are distributed to schools or other test-centres, many more people potentially have fleeting access; sufficient to take pictures and later sell them online anonymously a few hours or days before the exam.

I suggest that this could be greatly mitigated if the leaked papers were of lower utility.
One way of doing this is to convert the current uniform test paper into a family of similar papers. I propose a combination of methods to do this efficiently:

Firstly, the number of different types of question is increased judiciously. This stage is probably the most expensive part of test development, plus it has effects on the test 'normalisation', so this extension is the most limited in terms of number. (I think a 20% increase may be enough to start to benefit). However, one potential side-benefit is that more of the curriculum is potentially examined.
Secondly, for each of these 'base' questions, a number of variations is created. This starts by varying any values or variable symbols, inconsequential changes in formatting and so on, to create perhaps 10 unique variants of each question. Each of these is manually vetted.
Thirdly, the positioning and/or ordering of the questions may be varied in a manner intended to avoid any inferential cost to lawful students, but maximise the psychological cost to cheats. For example, in a series of questions, it may be desirable for one question to follow another - because answering question (1) is intended to prime the thought processes needed for (2). However, it may not be important whether a question is at the top or bottom of the page - except in that if you've seen a leaked paper, having it in a different position might throw you.

In the initial stage, I suggest that each test-center be given its own specific paper. This provides most of the protection, and also has the fringe benefit that the source of a leak can be localised. This improves the chance of identification and prosecution, further reducing the risk of leaks occurring. At this stage, small identical print-runs can be made, avoiding an abrupt transition to full individualised exam-papers and marking procedures.
Once this process has been established, the obvious development is to extend the process to give each student a unique exam-paper.

Scoring is complicated slightly by the need to add an additional layer of normalisation - based on which questions were present, but this is fairly tractable assuming a sufficient number of examinees.