Some companies doesn't allow an uploaded ID scan to be altered, so how could I protect myself in this case ?
Which companies do not allow this? I would not do business with a company like that.
I usually send my ID to companies, with the words "For company x use only 20/9/12" printed across the document, including across the photo.
However, I would like to know how other people encrypt their identity document and send by email, if the company does not have a public key? Sometimes I have used winzip, but I dont think its very secure.
I was thinking, would there be possible to have some kind of 'invisible' watermark on the uploaded documents, which could be spotted (by a program for example) if the document ever were to be lost ?
Invisible watermarks are no good, unless other companies look for them, when the ID is presented to them, for account opening.