You can use Autoupload module
AutoUpload is a user interface (UI) enhancement that initiates
automatic upload of files minimizing the number of clicks required by
Currently, users must select files, then press the "Upload" button. We
found users often don't realize a button press is necessary and
mistakenly think their image is uploaded when it's not.
This module removes the extra button press and hides the "Upload"
or you can check this post.