"images in Ookaboo are public domain or creative commons and can be used freely for blogs, web sites, schoolwork, publications, and other creative projects."
Purdue University's OWL (Online Writing Lab) contains relevant information for students pertaining to academic writing. This part of the site (Research and Citation) specifically outlines different formats for citing and referencing (such as APA and MLA).
This very clear pdf helps teachers figure out what they can and cannot ethically put on their websites. Great classroom resource for teaching about cyberethics too.