I suspect you have the Canon PowerShot SX610 HS because it is a 20.2 megapixel camera and there is no Panasonic camera with a similar name.
Most digital cameras have an option in the menu to change the aspect ratio.
Changing the aspect ratio to match each painting might be more trouble than it's worth. It is very easy to use a simple photo editor to crop the photo to the exact size of each painting.
On page 40 of the Canon PowerShot SX610 HS user manual it tells you how to change the aspect ratio from the default 4:3 rectangle to a 1:1 square.
