There's no authentication of you besides your user name, so any attacker could just take the user name you submitted, give it to the bank, then show you the "security image". Classic Man in the Middle attack.
DRM is bad, agreed—but monopoly is worse. If you buy a Kindle, you are buying into a scheme where you can buy media from only one vendor, and your media is not likely to ever be readable anywhere but on your Kindle.
That's no more true for a Kindle than it is for an iPod.
If you buy DRMed books from Amazon, then those books won't be useful on other devices. But, just as there are many sources for un-DRMed music, there are many sources for un-DRMed ebooks. Use one of them.