These sites have images you can use without the guilt!  "Click" on the links...    
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UNSPLASH  -  https://unsplash.com/

STOCKVAULT  -  http://www.stockvault.net/

PUBLICDomainPICTURES  -  http://www.publicdomainpictures.net/

MORGUEFILE  -  http://www.morguefile.com/

Wikimedia Commons  -  http://commons.wikimedia.org/wiki/Main_Page