I've been looking through a couple of databases for certain kinds of images, and realized that while I'm quite familiar with text/journal databases, I really can't say the same about images and photos. So I was interested to see whether people have go-to databases when they're looking for images and photographs. What I'm currently specifically looking for is photographs (or art, I suppose) of children in Europe around the beginning of the 20th century, but this is more of a general inquiry about the kinds of image databases people use for their academic research. :)
A couple of useful ones I've found are:
www.artstor.org - For art and installations from museums, mainly; didn't help me specifically, but seems really good if your topic of research is Art History.
The AP Images database - a lot of more recent photographs, as you might imagine, but still a number of good ones from the past as well.
Catalogue of Art Museums Images Online (CAMIO) - Exactly what it sounds like. I found the search function quite useful on this one, although for the specific subject I'm looking at the scope was quite limited.
There are of course also a lot of digital archives at US universities which I'm sure are excellent, but which tend to focus on US history, so I've avoided for my particular purposes.
Unfortunately image databases, on the library side, are rare. Item-level indexing of images, pre-internet, never happened on the level it did for text objects (all of the academic databases when they first came out were built on the backs of old pre-internet work in printed bibliographies and indexes). And you can't exactly full text search photographs, though of course Google is giving it a good go, so maybe soon! But images all have to have their metadata created by hand. Usually in the archives, it's by grad students, to make the metadata for all those little one off archives-specific Omeka and CONTENTdm databases you know about. Large scale database efforts tend to focus on art history, because it'll get the most use and the most academic librarians to buy it, and therefore be the most viable. Also Europe lags behind the US in rah-rah-scan-everything initiatives, whereas there's intense pressure here for us to put images online. So that's why Artstor is so lonely out there in the database world!
Sounds weird, but Flickr is a place to try, because a lot of libraries and archives (including non-American ones) upload their images there for discoverablity. If you set the license filter to creative commons that helps limit it down to more historic things, but not completely.
Honestly though I normally I use... Google Images. If you get the keywords right it'll turn things up, but you have to do some footwork to check to see if the images can be traced to any legit source, which is annoying. You can add "site:.edu" to the search for a little better results sometimes.