How do you recover overwritten files?

Question

my husband accidentally replaced an existing folder (all my photos)with the external hard drive back up. is there any way that i can get the original folder?

Answer 1

That's sounds like a horrible mishap. Your answer leads me to believe that yuo don't have some other backup. What about Time Machine? When it is set up in the default way, it backs up everything every hour, copying everything that changed in the last hour to an existing backup. Please tell me you have Time Machine!
The problem is that there is something called a "file catalog" that explains to your computer how to retrieve files from the disk. It connects all the photo files (many individual files, no doubt) to that (now overwritten) folder. Computers don't write files to the disk in just one place: a given photo file may be written in little bits and pieces all over the disk. The "catalog" also explains to your computer how to find all those bits and pieces when you ask it to get one single photo and display it on your screen. [I have never fully understood why this is how files are stored ...] So when the folder was obliterated, all your photos are actually still physically on your disk in many different pieces and places, but the information is gone that enables your computer to know where to get all the pieces and assemble them into a photo.
If there are still chunks of photo files that are intact, there are programs (one that comes to mind is called Data Rescue -- these programs cost $100 or so) that try to scour through the disk and copy all such files it can find, even though the catalog has been overwritten by your husband's mistake. Various 'rescue" companies will charge hundreds or thousands of dollars to physically scour over a disk to copy all the bits it can. People usually use them when a disk has crashed and cannot be mounted anymmore, but the platters are still there.
It is possible someone smarter than me will chime in here with some alternative suggestion. I am truly sorry that you have had this terrible mishap. Yuor husband owes you some sort of very nice valentine's present to make up for this (maybe an expensive sports car?). Your loss of photos hit home with me because my daughter is a budding photographer with about 150 GB of digital photos and because she would be devastated losing any of them, I make her use Time Machine and whenever she comes home from college I make copies of all her photos on various external hard drives. We have thousands of other photos and I have them copied to multiple external drives and multiple computers as well (in iphoto libraries).
Did you use iphoto for your photos? If so, you might stop using your computer (to avoid further overwriting anything) and see if Data rescue or something similar can find the iphoto library file/folder that contains the photos and try to 'rescue" it.