There is something wrong with a bank not wanting you to take pictures of cheques written to you before you send them off for processing. Its also very odd that they couldn't just stamp them and give you a receipt of sorts. To just take them willy-nilly, and mail them, with no record what was in there, sounds totally off for any bank.
I'd escalate the issue with them internally for now, but they aren't going to give you any money based on cheques they don't have (or have lost).
A cheque is a promise to pay, its nothing more than an IOU but which is governed by the Bills of Exhcange Act.
http://www.canlii.org/en/ca/laws/sta...985-c-b-4.html
The cheque has no inherent value. The problem is, someone could take the cheque, pretend to be you and cash it, or fake your signature on the back endorsing it, then cash it themselves. In either case, if they were successful, the money comes out of the person's chequing account and it may not be possible to trace who actually received the money.