How does plugin create pictures?

Hi

On your WebP images addon, does it generate the images in the webp format with every request (and use processing power) or does the images exist in the file system?

Thanks,

1. Customer opens the picture URL than plugin checks if this webp picture is on HDD
2. if web picture is not on HDD than plugin creates webp picture and store it on HDD
3. Customer opens the picture URL than plugin takes it from HDD