Bosch cameras with IVA or EVA can do that in-camera and it's got some interesting options. I did a very quick video showing setup of a basic "tripwire" that filters for human-size, human-shaped objects travelling at human speeds:
(sorry, forgot to enable mouse pointer tracking)
The one in the video is the affordable Starlight 6000 NIN-63023, with the basic Essential Video Analytics package. The combination of filtering for size, speed, and aspect ratio (plus good low-light performance) might make it a useful group-master trigger cam if a person were using
Blue Iris and had BI get alerts from the camera's own video analytics.
Notes for those entertaining this option: assume you'll need to buy the mount separately unless you know it's included, another US$25ish. The 6000s come in 720p and 1080p (the 63023 is the 1080p variant). Not every Bosch camera has the fancy analytics package (the basic variant is called MOTION+) but all the 6000s do. Oh noes, it is a dome camera and will attract dirt, etc.
Also note that on a 6000, the camera has onboard sensors that tell it its current tilt/rotation/angle and focal length. Tell it the mounting height and it can self-calibrate the analytics, so it understands what the actual size of an object is at any point on the ground plane it's viewing; this is key for the Video Analytics to recognize what's what. The calibration is in the camera's menus under Camera > Installer Menu > Positioning, and
the key piece you provide is the mounting height.
Not bad for a $200-$300 varifocal starlight cam
![Smile :) :)](https://cdn.jsdelivr.net/joypixels/assets/8.0/png/unicode/64/1f642.png)
It also has alarm inputs and you could add a PIR sensor that further limits false alarms, by only arming the video analytics when the sensor trips. For this option, you'd switch your Alarm VCA mode to Event Triggered, then tie it to your external PIR sensor as Alarm1, with your EVA rules enabled by it.