Round 1: General phone screen interview with CTO.
Round 2: A computer vision/image processing task. Tests your real domain knowledge, C++ and other open source libraries like OpenCV, QT acquintance, software development skills and Visual Studio experience.
Round 3: Code Review plus technical Computer Vision questions with senior engineers on Skype. Expect 45mins to 1 hour of interview. This round could be full of questions and will test your problem solving skills, technical aptitude and domain knowledge/experience, C++, OOP.
Round 4: If you made into this Skype round, Congratulations. Expect behavioral questions and brief talk with CTO. If you do not reside near Virginia, this round substitutes for an on-site interview. Later, you will get the video of an office environment in your email since it is a startup.
Overall interview is very +ve as engineers will throw you hints if you are stuck.