Doesn't work

I’m running on the latest version of WordPress and I just downloaded this plugin to give some effects to my images.

Looks like a great plugin…unfortunately, it doesn’t do anything for me. I enter the fields to give the image rounded edges and a drop shadow and it doesn’t change the image anywhere. Clearing cache and forcing to regenerate image doesn’t work either.

What could be wrong?

https://ww.wp.xz.cn/plugins/roundit/