I have a blog. I want my posts to be accompanied by online pictures. Which pictures can I legally take? For example, I just looked up Ross Douthat and came up with pictures from blogs.villagevoice.com, nytimes.com, and lectures.princeton.edu , etc. but I simply don’t know which ones can be taken according to American law and stuck on my blog.
Legally, every single image is copyrighted and legally the only images you can use are ones that you shot yourself, hired someone to shoot, or have an alternative copyright assigned to it, like Creative Commons (like most images on Wikipedia). The only images that are public domain are ones that the copyright has expired, were published before 1923, works produced by the United States government (like NASA images) and a few other exceptions.
Practically, unless your blog becomes very popular or you make enemies, you are unlikely to get into any trouble by copying and pasting images. But I would avoid using any images from sources that have loads of lawyers - and the three websites you mentioned have tons of lawyers. Don’t use those.
If you wish to use an image of Ross Douthat, you can freely usethe one on his Wikipedia page.
Using either Google Advanced Image Search or Flickr Advanced Search, you can search for CC-licensed (or otherwise free to use) images.
As mentioned, Wikipedia and its sister media storage site Wikimedia Commons are also good free-image repositories.
The other big exception, of course, is when you have the permission of the copyright holder, (which may or may not require a license fee). Most professional photographers will charge, but places like news sites and amateur photographers are often willing to let you use their images for nothing more than a credit in the right place. It never hurts to zip off an e-mail and ask them.
For photos of particular people, particularly celebrities, this will often net you a stock “publicity photo” and permission to use it on your site if you ask politely.
If all else fails, just link to the photos in situ. Your readers will need an extra click, but you can avoid the whole ownership issue and still make the material available via the original site.
Whatever you do, regardless of license, please make a copy of the image you use and serve it from your own server (unless the owner specifically asks you to do otherwise). I personally don’t want people using my images at all (at least not without asking), but I’m especially irked when someone embeds an image in their page, pointing it at my copy. When people do that, I usually replace the image with something else (typically just a really gaudy graphic with my URL in it). Some people are nastier and replace it with porn or the like.
What does this mean?
He means link to the page that has the image on it. That way any advertising is still displayed, so you aren’t stealing bandwidth, and you can see the image in the original context, so you aren’t plagiarizing.
I actually would go one step further, and link to the Google Images version of the page, so that you can see image you’re supposed to be looking for. And, heck, once the page loads, you’ve gotten all the advertising and established the context that it’s on another page.
You may be able to get away with fair use/parody use of the photos. This is why blogger PerezHilton always puts those white lines and comments on those photos. He was getting flack about stealing photos, now he claims these are parodies and he’s using the photos to make a point.
Of course as soon as his blog/website got super popular people for the most part stopped complaining because their photos were getting exposure. Photographers who were screaming “He’s stealing my photos” now are saying “My photos are so good Perez Hilton is using them.”
See it works both ways 
If you use someone else’s photos will you get sued? 99% chance -> NO. Yes they could use you and they’d be right, but that is time and money. They send a cease and desist letter first
In regards to the OP’s specific question, the photo at the wikipedia page he linked to is specifically listed as being available for reuse, so that’s a great place to start.
I’d just like to chime in with a couple of thoughts. First of all, using other people’s pictures without permission is obnoxious. There are millions of public domain photos and their easy to find. Just because you can find one of my vacation photos on a google search doesn’t mean it’s cool for you to use it to illustrate a story at your blog. Even if you don’t respect copyrights, that’s just not cool.
Secondly, if you do use someone else’s photo, you should give credit to the source with a byline or something similar. Again, even if you don’t respect the owner’s rights, this helps other folks figure out where the photo came from.
Actually, there are almost no public domain pictures of modern individuals. Where would they come from?
There are photos with Creative Commons reuse licenses but these are NOT, not, not, not, in the public domain. People often confuse these, but the differences are very real. There are several levels of CC licenses and they have different levels of restrictions of how you can use, alter, or reproduce the original. If you do use a photo from Wikipedia make sure to check the fine print under the photo. You may find that you can only use it with attribution to the original photographer or source. This would not be true for public domain pictures. (Yes, it’s always polite to give credit. That’s a different issue from whether it is mandatory to give credit.)
One other point that applies to the overall subject, though not to pictures of individuals. It is generally considered fair use to reproduce a book cover, album cover, product box, or product when discussing that product, just as it is generally considered to be fair use to reproduce a press release. There are fine points to this, and very little has good case law to back it up, but in general it is OK to use a picture of a book, but not OK to use a picture of the author.