Can I use workers without routing traffic through Cloudflare?

I can’t update my previous question about being utterly lost on how to add watermarks to our images.

Before I waste more time and hair on the awful documentation, can someone confirm or not whether I can use workers if I’m NOT routing my traffic through Cloudflare?

I was told in my other question that I should copy an example worker and create a route.

All I’m doing is using Cloudflare Images to upload 100,000+ images in order to serve them on our website. Surely it’s possible to add a watermark to images in a simple way?

I’m coming from Cloudinary where it is quite easy to add a watermark just by adding options to the URL and the documentation is very good.

I hope I haven’t made a massive mistake and wasted dozens of hours uploading to Cloudflare.

Can someone help?