The first question in every deployment is whether the installed cameras are enough. In most cases they are, and the budget goes into edge equipment rather than replacing the fleet.
Resolution matters less than assumed
A person-detection model works on crops between 64 and 128 pixels tall. With a 2 MP camera at eight metres, a person occupies roughly 90 pixels: enough. Moving to 4 MP does not improve detection; it multiplies compute cost and network load.
The angle does matter
The common mistake is reusing cameras mounted for surveillance, aimed almost horizontally at the door. In that geometry people occlude each other and counting degrades as soon as there are two rows of visitors.
For counting and occupancy an overhead or near-overhead angle works best, between 60° and 90° from the floor. Where an existing camera cannot provide it, the answer is not to replace it but to add a unit at the counting point and leave the original doing surveillance.
Decision criteria
Before quoting equipment we check three things about the current installation: mounting height, angle relative to the floor, and available light at the worst moment of the day. That is enough to know which zones are covered and which require an additional camera.