You cannot write to a camera through the USB cable.
The camera treats it as a one way street; from the camera to the computer.
The camera does not want any outside source to write to the camera.
If you have a card reader/writer, you can write to a memory card.
But, it is unlikely that the camera will see anything that you add to the card. When the camera writes to the card it also updates the FIB (file information block) on the card, so that it can keep track of the pictures it takes.
Also if you have ideas of taking a card from one camera and putting it in a different camera and taking more pictures to that card, you can get into trouble. Being two similar Canon cameras, it might work but I would suggest you make sure that you have a back up copy on the computer before trying it.
The proper way to reuse a memory card from a different camera is to copy all the files to your computer.
Then Format the card with the new camera before taking any pictures.
The Format will deleted all pictures on the card.
If you want to carry around pictures for others to see, I suggest you get a multimedia player.
I have some pictures, which were taken with a Powershot SD700 IS digit camera. Would like to transfer the pictures to a new model Powershot SD 950 IS.
Tried to transfer the pictures using Canon Camerawindow application. However pictures will not transfer to the Powershot SD 950 IS.
Can I, or how do I transfer photo's from a older digit camera to a newer model. Please help!