Martial arts online has been a controversy for many years. However, it is now becoming very accepted just like taking classes online. Recently, I have been teaching many students from all over the world and it has worked so well that we have been able to expand our teachings.
Through SKYPE we are able to see exactly the forms and the techniques that are produced by the student. A student can not advance without a full understanding of the form or the technique. In the past 30 years, it was not unheard of a student sending in a video to be tested for a belt and many systems did this.
Thus, teaching martial arts and karate online is no different. However, I suggest a Sensei that is experienced in this as it is a different teaching methodology. Thanks for your questions.