iCloud & iCloud Photos · iCloud Photos and the Photos library
Why didn't deleting photos free up my iCloud storage straight away?
Short answer: Deleted photos sit in Recently Deleted for a while so you can recover them. Open Recently Deleted in Photos, select them and choose Delete to release the space now — but then they're gone from every device for good.
Deleted photos go to the Recently Deleted album first, where they can still be recovered for a while. To release the space now, open Recently Deleted in Photos (you may need to unlock it with your password or Touch ID), select the items and choose Delete.
Once deleted from Recently Deleted, photos are gone from iCloud and all your devices and can't be recovered, so be sure you have copies of anything you want to keep. See recovering a deleted photo.