I uploaded bevel.js in the zp-core/zp-extensions/image_effects folder.
Configuration still gives: bevel.js not present.

What am I doing wrong?

You need to to place the image effect file in a folder named image_effects and place that folder into the plugins folder. (in the root of your install)

You must never change anything in the /zp-core/ folder.

I found the error.

Some paths in the bevel.txt (and all other filters of that brand) pointed to the wrong folder:

/%WEBPATH%/%USER_IMAGE_EFFECTS%/

instead of

/%WEBPATH%/%ZP_EXTENSIONS%/%IMAGE_EFFECTS%/

Works perfect now!
(Thank you for your reply)

it should actually read%WEBPATH%/%USER_PLUGIN_FOLDER%/image_effects/bevel.js to work in the /plugins folder (and does in the example bevel.txt I have). NEver put anything withn /zp-core unless you want to do it again on every update.