To add an image to a question, all you need to do is add a Content Block on the question page inside the Quiz Builder
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Inside the Content Block click the option Include Image. You can add your own or use one from Unsplash
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You can adjust the image width and if you're adding extra content like text, you can also adjust its position relative to it (at the bottom, to the left, right or at the top of the text etc.)​

Just hit 'Save Content Block' when you're finished.