Online Image
If there's no date, enter: n.d. If there's no title, create your own title.
Smith, J. (Photographer). (n.d.). Lemons in a bowl. [Digital image]. Retrieved from http://flicker.com/lemons
In text entry:
Online Image (no creator/photographer listed)
Title of image [Digital image]. (Year). Retrieved from URL
Umbrellas on the beach [Digital image]. (2012). Retrieved from http://flicker.com/umbrellas
In text entry:
(Title of image, 2012)