The answers to the two preliminary questions are:

1. The average human hair has diameter 50 microns, which converted to nanometers is 50,000 nanometers (recall that $1 \mu \textrm{m} = 10^3 n \textrm{m} $).

2. A ream of paper containing 500 sheets is approximately 10 cm tall. So, since it contains 500 sheets, we deduce that each sheet has thickness 0.02 cm, which converted is 0.2 mm, 200 $\mu$m or 200,000 nm.

Now, in order to create a robot camera, one would need to inject it into a human's blood arteries, and it would need to circulate with ease around them. The coronary arteries are among the narrowest arteries in the human body, so there is no need to go into even smaller dimensions.

However, we do need to bear in mind that the camera is being built for the purpose of identifying whether the arteries are becoming blocked, and therefore we might want to ensure that it will be able to circulate inside, even if this is the case. An artery is consider to be in a critical condition, if more than 75% of its interior is filled by a thrombus (i.e. a blood clot which blocks blood circulation). At this stage, the patient already has symptoms, so the detection is not really necessary. Still, in order for a camera to be able to circulate freely inside the artery, it shouldn't be wider than 20% of the artery's interior diameter, which means in our case 0.1 mm = 100 microns.

Since nanotechnology, and in particular nanorobotics, has reached the stage where robots with dimensions of order of nanometers are now being created, such a robot camera, would be possible in principle. Of course, though, this is simply a theoretical thought and chances are that nanorobotics will need to advance a lot in order to generate such devices.