Note; I use female pronouns for the submissive, based on my experience. Obviously all other pronouns can apply. Some anatomy may not.
Based on conversations with submissives and posts on various sites, I think many online Doms insist on viewing a submissive live as she does a task or have her make a video. These are required as “proof” These can be misused of course. The most extreme would be selling them as porn. In my view, this is using a submissive as entertainment for the Dom, rather than showing obedience.
Let me talk about one important element of submission, nudity. It is practically a tradition of BDSM . I prefer a submissive to be naked for most tasks as a sign of her submission. If I want a sub to be naked for hours a video is useless, because it is for a few minutes. A complaint about being cold or a request to be allowed panties is a better verification, in my opinion.
Obviously a sub cannot be nude in public. A good substitute is having her go out with no panties on. Especially in a skirt the sensation on her ass and pussy are noticeable. Obviously no proof is possible. I did once order a student to go to class without panties. She refused, which in a sense was proof that she was obeying me for her other tasks.
I usually require a sub to spank or whip various zones of her body. Yes, I could watch and count the strokes, but her description of her ass and the pain satisfy me that she was obedient. If she offers pictures of her marked body, I do not turn them down of course. If a picture is requested I want the sub not to view it as “proof” but as reinforcement of her submission to my task. In another sense it is not “proof”, because I cannot tell if she delivered all the strokes I ordered.
There many other things that I require a sub to do where I can evaluate her obedience by her written report. If a sub cannot have a butt plug in her house for privacy reasons, her finger is a good substitute. I tell her to lubricate her finger and insert it while she is in the shower. Trying to take picture would be crazy. When she tells me how it felt, I know if she did it. ( My point of reference is my own finger up my own)
I could go on, but I think I have made my (slightly radical?) point of view on online Domination/submission clear.