Google Images is a quick and easy way to find lots of images from web pages across the globe. But it only searches web content that it can find -- many images are actually hidden in databases or archives. The quality of images - size, resolution, description, usage rights - also varies considerably on the open web. Use Google, but don't rely on it for all image searches.
Google Image is one of the easiest to use image search engines. One advantage is that most people are already familiar with using Google. So even if you never searched the image part of Google, you should be comfortable using it.
Another advantage is the advanced options in Google Image. It is easy to control what images your search for. You can limit the size, the ratio (vertical versus horizontal), colors, image type and usage rights. If you forget to limit before you search, you can also limit afterwards.
While Google Image is a great tool, keep in mind that it is not perfect. First, it pulls from various web pages. While *most* of the images you find will be what you are looking for, there will be some irrelevant ones that sneak in. In some cases, it may pull pornographic images, even with filters on. However, how often this happens does seem to depend on what you're searching for. The more common the search term (e.g. "dog" or "horse"), the less likely to get something irrelevant.
Another problem with Google is the usage rights. You can limit to specific usage rights (i.e. images that you can use) from the advanced search; however, you cannot limit after you perform a search. Another problem is that the usage rights are imperfect. Even is an image is returned as "available for commercial use" or "labeled for reuse," make sure you double-check the original site. There are several blogs and web pages that make use of images that are not theirs.
Reverse Image Searching
To do a reverse image search in Google Image, click on the small camera icon in the search bar. This will give the option to upload an image or enter an URL of an image already on the web. After you enter an image, Google will either tell you what the image is or show you similar looking images. This is a good way to browse images in a particular style.