The question you asked possibly will not get any helpful answer, as there is no company providing cloud storage real-time annotations without allowing to download the document on your system. I think not yet such technology developed to support the real-time annotations with cloud storage or online based data storage system.
Real-time annotators can annotate the object in the image if they have uninterrupted and high-speed connectivity of Internet and servers where such data have been stored. As on real-time annotations objects can be moving or processed for other needs becomes difficult to annotate on real-time basis and accessing the same image by multiple users can also disturb.
Hence, real-time annotation not seems possible right now, maybe in future such technology get developed and companies will provide the real-time annotation service on cloud-based storage service even without downloading the documents. But right now you get live real-time annotation services that will help you to get the quick annotated images as per your needs.
Cogito is one the data annotation companies providing live annotation service for machine learning and AI model development. You can send live images as per your urgent requirement and Cogito annotation team will give your the outputs without stipulated time period. The quality will be not compromised while meeting the deadlines as, it offers real-time annotation with scalable annotation solution at flexible pricing for various industries needs.