Preview app security: How does cropping work?

When you crop an image in Preview then resave the newly-cropped image, what happens to the part of the image that was cropped off? Is it marked as recyclable and "sent" to the trash, so that when you secure-empty trash it gets erased? Or is it maintained on the hard drive (along with the rest of the image that hasn't been cropped), but now just marked as non-displayable?

 

If you Save (CMD-S), as opposed to Save As New, the newly-cropped image, and you subsequently secure empty trash, do those cropped pixels get written over? I don't know how Save works. Does a Save command cause the currently active image data to be COPIED to a new physical location with the old location being marked as dead, or does it leave the data in the same place but move the start-here and end-here tags for the active data? If it's the latter, does a secure empty trash command include the cropped out data in the secure erase?

(I suppose this question applies to other software as well, such as Pages and other word processors, although I guess different programs may vary in how they deal with these issues.)

 

I suppose, in a way. But not so much a history as the actual data itself. When you crop, does the data get destroyed once you secure-empty trash or is it just hidden from view? Could the data be reconstructed after a secure-empty trash using data-recovery software?

 

Thanks for the response.

(It's not that security has been such a concern, I am just curious about the process. And still running older hardware and software, so no File Vault 2 or SSDs.)