With Notifications you will be able to discover who has published your image.
To discover which images have been published:
Go to your profile and tap on the Notifications icon.
Tapping on each notification will also bring up a list of all the Collections this image has been published to.
Please note: You will only be notified when an image is published to a Collection, not when your image is saved to their Saved Images. Your images will always be attributed to your Profile. Your images cannot be saved to a Camera Roll or Gallery, and cannot be used outside of Collections.