If a file is listed under the Creative Commons Attribution-NonCommercial-NoDerivs (BY-NC-ND) License, you may redistribute this work non-commercially, as long as you credit the artist by linking back and pass it along unchanged and in whole.
Again, NoDerivatives means if you remix, transform, or build upon the material, you may not distribute the modified material.
Under this license you must give appropriate credit. This means: if supplied, you must provide the name of the creator and attribution parties, a copyright notice, a license notice, a disclaimer notice, and a link to the material.
Here's a perfect generic example of attribution (modifications are necessary for each license):
"Creative Commons 10th Birthday Celebration San Francisco" by tvol is licensed under CC BY / Desaturated from original