Does anyone knows what exactly happens behind the scenes when Mac OS X verifies a disk image (.dmg) file? Is there any way to extend or customize the procedure? 

EDIT: I would like to create a disk image that verifies that it does exactly what it should do and nothing more. For example, if I distribute some software that manages passwords, a malicious user could modify my package to send the passwords to an unwarranted third party. To the end user, the functionality would appear to be identical to my program, and they would never know the package was sabotaged. I would like to perform this verification at mount time.