switch statement

i have a picture of a white box with a black border around it.
when i push the ‘load’ button i want a picture, with an actual image, to overlap that white box.

so there are simply two pictures and a button.
when the button is pushed a copy of picture ‘A’ overlaps pictures ‘B’.

can anyone produce a very simple code of this.
any help is much appreciated. thank you!

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