I need some explanation. I have installed a SP Smush Pro

Hello,
I need some explanation. I have installed a SP Smush Pro plugin.
Everything is fine, but I can't use the plug-in overtime, because it's too expensive for me.
I need to understand what happen to the image that I have "smushed" with your plug -in when I stop the payment.
I mean, I need to uninstall the plugin?
Or I need to left the plug in installed and use another way to optimize my pictures?
What Happen to my image when they are smushed? The original file change or remaining the same and use a copy of them?
Please help me to understand. I'm a little bit scared for my pictures