It is really a good habit to back up everything important well. You should always keep on doing that.
But, now, it is also possible for you to get back these photos that have not been backed up as long as you've not rewritten them with anything new.
What now you should do is to opt for a proper memory card data recovery freeware for your photos. In fact, there are many similar data recovery freeware available online. You should make your own decision after doing much researching over the internet.
But, if you don't want to get so many troubles, you can directly try some memory card data recovery freeware to take chances, such as Recuva, TestDisk and iCare Data Recovery Free, etc.
Good luck!
Hello, I need help!
I stupidly deleted all images off from my Nikon camera memory card. Even though I had backed them up on a hard drive, there were still some photos that had not been uploaded to this backup drive. So, is it possible to recover them? What should I do next? Please, help me!

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