It can happen but it is not always necessary. As stated above, there are issues with photos so you have to be very careful about what you send to someone you do not trust.

There are other methods to 'prove' a task has been done. You could, for example, have someone write a detailed report on what they did. It is sometimes very difficult to properly describe sensations you have not experienced so if you ask for a detailed, emotional and descriptive report it is possible to sometimes spot faking. There is also audio and live webcam or live messenger chat.

None of these really 'prove' that you have done something as they are all (yes even photos) possible to fake. But they make the sub feel as if they are actually sharing with the Dom/me. it is not so much about proof but rather that feeling of kneeling in front of the Dom/me and telling them how you felt doing whatever it was you did.

It ultimately comes down to trust... do you actually trust that person with your information? BDSM should be about two things - communication and trust - and LD/Online relationships especially need both things to be present in excess.