Creative Commons is a non profit organization providing infrastructure, a set of free copyright licenses and tools, that creates a balance inside the traditional “all rights reserved” setting that copyright law creates. Creative Commons licenses are not an alternative to copyright. They work alongside copyright to enable authors to modify terms to share their work while still retaining copyright.
Creative Commons has developed a search portal that allows you to find CC-licensed works through sources like Google and Flickr. There is also a best practices for attributions for any reused CC content.
(This information is excerpted, with modifications, from the Creative Commons website.)
Plagiarism of images is really no different than plagiarism of words, music, or any original work. Copying an image from a book or the internet without citing the original source (or gaining permission of the creator when necessary) constitutes plagiarism. Plagiarism is academic fraud with serious repercussions. See the Libraries' Plagiarism guide for a full overview of UK's policies and penalties regarding plagiarism.
All too often students make careless mistakes that lead to accusations of plagiarism. Without intent to cheat, they lose track of citations in the course of research or may not understand that simply copying a few sentences from an article or pasting in an uncited image found through Google Images constitutes plagiarism.
It is thus very important to be vigilant about citing sources and, in the case of images, knowing what the creator requires when reusing their work in the academic setting or the private sector. Sometimes there is a fine line between plagiarism and fair use of images so take care to determine any copyright restrictions associated with images you wish to reproduce.
Compfight is an image search engine tailored to efficiently locate images in Flickr for blogs, comps, inspiration, and research. Compfight employs filters and options designed for discovering and locating images in the most efficient way possible.
To really take advantage of the Compfight experience, you will need to get familiar with the Creative Commons, and understand each license type. Please always double check licenses before use.