[icebraining]

You should pre-populate the images with stock photos found on google images.

That's copyright infringement. Just because they're available on Google Images doesn't mean you can use them on your own site.

[wmeredith]

You can ping Google images for images filtered by licenses.

[icebraining]

That's useful as a tool for a manual search, but you can't trust it by itself, since sites can tag any image as CC. In fact, you can find very well known -and definitively not CC licensed- photos on that search, like World Press Photo winners or Leibovitz's.

[pkamb]

"found on <some service>" then.

[onedognight]

You can just link to the image on the original site. No distribution means no copyright infringement. Rude yes, illegal no.

[icebraining]

Illegal no

I wouldn't be so sure: http://news.cnet.com/2100-1030_3-6145744.html