The smallest micro cameras are initially developed by the mobile telecom and pharmaceutical industry, but the developers of spy cameras make good use of this. Due to the continuous improvement and reduction of the camera lenses, a camera can be built into more and more utensils and with the current developments the end is still far from in sight. 
Today's mobile phones sometimes already have micro cameras with a 12MP lens and in the pharmaceutical world cameras are already used in medical procedures that are no bigger than a pin button.
Such cameras are not yet processed in the spycameras, but with some spycams this is pretty close. The only drawback of the micro cameras at the moment is the fact that the battery needed to power the micro camera is many times larger than the camera itself. As a result, it is not yet possible, for example, to incorporate a micro camera with battery in a screw.
In the near future it will probably be possible to incorporate micro cameras into shoes or belts in a way that the wearer does not notice that it is actually a spycam. Stay tuned ...
See viewing micro cameras already for sale? Look here for an overview of the spy: Micro cameras or here our newest micro camera
Also read our other blog article about: Micro cameras