I’ve posted earlier of EpocCam, which allows an iPhone or suitably-equipped iPad to work as a webcam via USB or WiFi. This is not a free app, costing around A$13 and uses downloadable drivers on the Mac.
A suitably-equipped iPad is any that has a FaceTime camera in excess of 1.2 MP. This excludes all standard iPads, even the new iPad 8. FaceTime cameras of 5, 7 or 12MP can be found on iPad Pros, iPad Airs & the iPad Mini 5th generation models. The first series of iPadAirs & 12.9 in iPad Pros also have the basic 720p 1.2 MP FaceTime cameras and offer no improvement over a Mac’s 720p camera.
The only Macs that have a 1080p FaceTime camera are the 2017 iMac Pro and the 2020 iMac 27-inch models. Having used one of the latter types I can say it makes a massive difference in performance.
Getting back to the subject matter: there’s an alternative to EpocCam called Iriun Webcam, which is free on the App Store, unlike EpocCam, it doesn’t use drivers as such. Instead there’s a free Mac app from the developer’s website that acts as a server when running.
Iriun webcam offers only two settings: you can choose between the front & rear cameras and to use the rear camera’s flash as a steady illumination source. It can connect via USB or WiFi and really, those are all the settings needed to replace/replicate a webcam. The extra capability of EpocCam, while nice to have, is unnecessary fluff.
Go to https://iriun.com/ to download Mac, Windows or Linux versions of the computer app. There are also links to the mobile versions from the Apple App Store & Google Play Store.