Same as all the others - I click on the transaction and BAM - an image of the check appears, front and back. I don't know that I've ever received the canceled checks themselves. That would confuse me.
I do read that Banks and credit unions are generally not required by law to return cancelled checks or check images, but that state laws require they hold onto the checks for 7 years. That's odd to me since they're being used to prove payments for divorce settlement, child support, or other required expenses.
I've never been in a position to submit check images, I've only used it to figure out where the money was going. If I were in your shoes, I'd run the transactions that need check images through a bank that provides images of the checks - maybe a national bank or credit union in another state that regularly requires canceled checks to prove payments?