Under Moral Rights law, you must provide sufficient acknowledgement of the work copied, identifying the creator / author and the work from which the copy is taken by its title and other description information. Acknowledging the source of your work also helps avoid claims of plagiarism.
A standard attribution statement should include:
For attributing Creative Commons Materials, please refer to:
Attributing Creative Commons Materials. Published by the Australian Research Council Centre of Excellence for Creative Industries and Innovation in partnership with Creative Commons Australia. Under a Creative Commons Attribution 2.5 Australia licence.
If you don’t know the source of the work, you need to indicate this with the following statement
'Source unknown. All reasonable efforts have been taken to identify the copyright owner of this material. If you are the copyright owner or know who they are, please contact firstname.lastname@example.org'.