images of my site url

I configured the plugin properly. but this plugin is adding at the end of the url of my images a stranger code.

and this I think is grabbing slower loading my site.

example. https://prntscr.com/8kqj0b

is adding a code? af9666

Why is this happening?

Thanks in advance.

https://www.ads-software.com/plugins/w3-total-cache/