All sorts of talk over the weekend about Google's image database is only updated twice a year. Yes, it's true. I'm sure Google will make some changes.
However, I hope that all this info once again reminds the searcher that only relying on one search tool (even Google) and thinking it's ALWAYS going to (don't assume) provide you with the material you're looking for, can cause problems. Yes, Google is a wonderful product but that doesn't mean others can't do it as good or better. Let the "search wars" work for you by learning about and using a variety of tools.
When Yahoo made an announcement about their image database (it also powers the AltaVista and AllTheWeb image search services) a few weeks ago I commented that Yahoo Image Search has been a first class service for a long time. If you haven't taken a look, you should.
Btw, this post also includes how to use Yahoo to search for only the latest news images.
There are thousands of specialty (subject focused) image databases out there. In some cases, they're able to provide you access to material unavailable from a gerneral image database (like Yahoo or Google) and also can offer options to search the material unavailable from a general web engine. It's impossible to list all of these databases but here's an idea of what I'm talking about.
When it comes to text searching and why using more than one engine might be a good idea, Chris has some comments in the SearchDay article: Exploring Search Engine Overlap. Since Chris wrote the article, Jux2 has started to offer an overlap comparison tool.