How to remove an image or movie from iDevice but not from iCloud Photo Library?
I assume your problem resides in the fact that Photos app is taking too much space on your iPad.

If this is the issue, your best solution for managing space and keeping a synced Photo Library across devices is to enable Optimise iPad Storage under Settings -> Photos &amp; Camera -> Optimise iPad Storage on your iPad.

The Photos app on your iPad will then manage which photos are kept at high resolution and which are just stored as thumbnails. You can also activate the same preference on your Mac's Photos app, under Photos -> Preferences -> iCloud Tab -> Optimise Mac Storage on the top bar.

Unfortunately, there's no way to delete a photo exclusively in one device once iCloud Photo Library is enabled.