Final answer:
The best detail suggesting the narrator suspected Hamlet of cheating more than once is B, where others kept images for weeks, hinting at an ongoing issue.
Step-by-step explanation:
The detail that best supports the inference that the narrator may have suspected Hamlet of cheating more than once is: B. ...images some of the girls at school were only too happy to have on hand for weeks afterward.
This implies a recurring issue that not only did the narrator know about but also one that was common knowledge among others. Being 'too happy to have' suggests the images were a result of a repeated offense, as they were used to document or highlight the cheating.