HTML5 lets you drag files from Windows Explorer or Desktop and drop them on a predefined area of a web page, from where you can upload them to the server using jQuery. Mmi Update 5150.

Take a look at - it will help you to understand how to implement javascript event when droping file on your page. When you have such event, then you just bind ajax call on this event and each time when this event fire sending ajax call to the server. It will not be asp.net request to server with all related stuff like transfering states, page reloading and so on, just a lightweight async call only with the data you need. If you want to have standard postback, call __doPostBack() javascript function which is generated by asp.net. Autotest 4 Pro Greek here.