I know what you and a few others below are saying about the user interface issue but this seems to be a data integrity issue and sounds like it is meant to solve a serious problem; mixing up medical records and making sure a data set for a study isn't corrupted. Depending on the situation this is a problem that kills a lot of people.

It's still not a perl question but with JS you can probably solve it in a few ways that the casual (non-technical, one-time) user couldn't get around while still being able to submit the form. Don't write the form at all unless JS is on and do some primitive checksum via onkeypress that writes it to a JS created hidden input field/node so you know that at least X characters were pressed in the same order in each field (or clear both and start over) and it wasn't a cut and paste. Then send the form and checksum data to perl on submit for validation.