If you are copying them to your computer from the SD card, then you may have them in 2 places on it, one in the place where you copy them and one in the 'photo stream', but it's the photo stream that you are looking at on it. For photo stream, from http://support.apple.com/kb/HT4486 :
On your PC, open the iCloud Control Panel for Windows and select the checkbox for Photo Stream. You can click on the Options button to verify that both My Photo Stream and Shared Photo Streams are enabled and adjust the settings. Be sure to click Apply
PC iCloud control panel : http://www.apple.com/icloud/setup/pc.html
Before you delete any photos that you've copied onto the iPad via the camera kit (assuming that you want to keep a copy) then make sure that you have a separate (non-photo stream) copy e.g. copy them from the photo stream folder on your PC to another folder on it, or copy them to your computer by connecting the iPad to it e.g. via the windows camera wizard : copying photos.