Since you said you were removing the memory card to download the pictures, I will assume that you are using a card reader to download to the computer.
If you use Windows Explorer to do the download, you must be "moving" the pictures instead of "copying" the pictures.
A "Move" will delete the original photos as it moves the picture to a new location.
A "Copy" will not delete the original photos.
When using "drag and drop" I always drag with the RIGHT mouse button.
When you drop the picture(s) at the new location you will be asked if you want to Copy or Move.
I have an EOS 40 digital Canon Camera and when I down load the pictures off my memory card onto my computer, the pictures no longer show up on my camera when the memory card is placed back in the camera. Do they automatically delet or is something wrong?
thanks for your help