There are plenty of extra safety measures you could add to this security setup.

For example, have a password protected folder through a 3rd party app like:
http://www.digitalcitizen.life/5-tools-password-protect-your-folders-windows
http://www.intowindows.com/top-4-free-folder-locker-software-for-windows/


This password protect folder would have 5 sub folders - each with their own separate password.

In each subfolder have over 1000 random images.
So a hacker would have to hack a minimum of 2 passwords (if he's lucky) or up to 6 passwords (if he's unlucky) to find the image with the key (that's password protected) out of 5000 different images.