Passport upload is usually also supplemented with other documents such as rental agreement/ State ID etc. In my experience, banks/ government sites ask for passport and people trust them enough to send them over. Thus apart from the upload experience, your platform has to evoke trust. However, verification of these documents is done by a human in the loop. So to answer your question.
There can be multiple scenarios:
people who already have a copy of their passport on their desktop: the web experience will not be much of a hassle for them.
people who click a picture of their passport to upload - the web app can have a mobile friendly version for this.
People have a copy of their passport but they are working on a public computer/ only have it on mail: As mentioned by Jeff Zeitlin, emailing can be an easy option.
User testing would help to formulate the solution even better.