Camera Roll Resetting Count?

I take photos on my iPhone 4 and transfer them. Lets say I take 20 photos with my iPhone 4. Those photos are titled IMG_0001-IMG-0020. When I cut and paste those photos into a folder on my computer, and start taking photos with my iPhone 4 again, the count resets back to IMG_0001, and when I put these photos in the same folder, they have the same name, and it prompts me to replace the current photos on that folder because they have the same name! Help?