I'm pretty sure you would get somebody's age, race and gender just by reading their resume/CV, which most job boards allow potential hiring companies to peruse.
The difference is how easy it will be for a candidate to make the claim that you must have known about what protected classes they belong to when you discarded them as a candidate.
If all you have is the CV, possibly anonymised, you can feign ignorance or genuinely be ignorant of the candidates age, race and gender in a way that will be absolutely impossible to pull off if you've seen them on video.
If all you have is the CV, possibly anonymised, you can feign ignorance or genuinely be ignorant of the candidates age, race and gender in a way that will be absolutely impossible to pull off if you've seen them on video.