I see many hubs with google images and yet I heard we are not supposed to use them.
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That's true, but you must still go to the website where it originally appears, double-check that it really is free, then cite the original source (i.e. not Google images). If you read Google's instructions it says so - but most people don't read it!
Other than rgb and free digital images...??? Thanks for the great response.
Flickr (click on Creative Commons when you search), morguefiles, freedigitalphotos.net, pixabay, wikimedia, & more. Here's a link. http://search.creativecommons.org/ Check the Learning Center, too: http://hubpages.com/learningcenter/legal-image-