If you look at the file names for each background, you'll notice they have numbers in them. If you make the image with an f-string for the file name and take in the inputted number as a variable, then you can put the number variable into the file name, which will help you get the right image.
The basic code to create an Image object is:
Therefore, each bgNum will store a different filename. You can create an if statement, which depends on the user's input to change the filename of the image object.
There is a file of choosing background color game, you could refer it to make users choose your backgrounds.