UPDATE 20 December 2012: Be sure to read Alan Levine's post about this.
Richard Byrnes alerted me to (yet another) new function of Google Drive: When you need to add a picture to a document or presentation you're creating in Google Drive,
- choose "insert image"
- then choose "search"
- then choose "stock"
"Thanks to your suggestions, 5,000 new photos of nature, weather, animals, sports, food, education, technology, music and 8 other categories are now available for your use in Docs, Sheets, and Slides. More than 900 of these photos were selected directly from your submissions -- we really appreciate your help!" (link)When you select a photo and insert it in your work, there is no indication at all of how it should be attributed. It's nice to be able to access "photos available for re.use", but they still must carry an attribution.
I searched for a "blue" picture, choose the one of the planet, and then did a Google Image search to see if I could find where it came from.
I found this advice on the Wired How To wiki:
Most stock image services provide royalty-free images for about a few bucks per high-resolution image.There's no one-size-fits-all attribution for stock images, so you must check the policies of the service you are using to see if and how you need to credit imagery.In general, however, a stock photo used for editorial purposes might be attributed as:©[stock service]/[username of creator]When using Stock imagess, the IFB blog recommends
Give CreditThese days finding the source of an image can seem impossible. You found something off Pinterest, it links to Tumblr, that credits Weheart.it that was some how sourced to FFFFound!, and that was linked to a blog post from way back in 2010 that linked back to Tumblr. Sound familiar? You can run an image search in Google, by dragging and dropping an image to Google Image Search, and it will pull every time it was used. You’ll still have to do a little digging to see what the oldest entry was, but it’s a good way to verify where the original source is. After running a search, and you’re not certain as to where the image came from, you can always give credit to the place where you found it, but specify that it’s not the original source. But always, always, always give credit where it is due, even when you have permission to use.
(Bold emphasis mine)