How do you delete files from your Mac? Empty the Trash can, right? That works, of course, but doesn’t actually delete the files from the Mac. Instead, the files remain, and all the Trash can did was turn off a digital marker which makes the files visible. Any one of a number of simple utilities can find files that have been deleted by the Trash can.
How can you delete files on a Mac so they cannot be found and resurrected? Either of these methods work, and both are free.
First, while in the Finder, select Secure Empty Trash… from the Finder’s menu. That method is built-in to OS X and writes over the files you want to delete so they’re difficult to recover.
Second, try the Incinerator app. It works much the same way as the built-in method, but gives you a few more granular controls over the process.
Select the number of times you want a file to be overwritten, and then click the Incinerator button. It works in the background while you do something else, but gives you a Notification Center pop up in Mountain Lion so you know the file has been, well, incinerated (digitally, of course).
The only caveat here is that Incinerator does not delete OS X’s Package files (iPhoto is a package file) which appear as a single file, but which are really folders which contain other files). Still, it’s a good way to delete sensitive documents, incriminating photos, or other files which could cause you grief if they fell into the wrong hands.