old photos on SD card are imported along with the new ones

I seriously can not understand why ALL my photos are being imported instead of just the new ones that haven't been previously imported. Until recently every time I would use windows import the only photos that would be imported were the new ones on my SD card. Now ALL my photos are imported and I have to sit through hundreds of ones being imported that were already imported. What changed and how do I limit only the new photos from being imported?

Thanks