How about a different approach?
If you provide a large bank of questions (100s or 1000s) that the quizzes draw from at random, then each learner/candidate effectively gets a different quiz. Even if they take screen shots, few of the questions will correspond to what other learners/candidates see in their quizzes.
However, coming up with high quality quiz questions is a lot of highly skilled work. I guess it depends on how far you're willing to go to prevent/discourage copying.
If possible, I'd recommend giving more "open book" tests/exams. Not only are they more difficult to cheat at, i.e. everyone's answer will be different according to their own understandings of the concepts and themes, but they also encourage learners to study the course material in greater depth and for greater understanding, and are more representative of learners' knowledge.