Spy cam manufacturers have been creative in producing some of the most cleverly disguised (and tiny) camera/DVR systems, complete with HD video, motion detection, large storage card support and remote controls...
1. USB flash drive spy cameras
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So how can you tell? The camera lens for these USB stick cameras is usually located on the posterior end of the stick, opposite the USB plug. With this form factor, this spy cam will blend seamlessly in an office or classroom.
See all 10 here.