These large databases contain millions of images on many subjects, almost all images are either in the public domain (made before 1928) and thus can be used without restriction, or made available under a creative commons license which allows free reuse with certain restrictions such as always attributing the creator.
Wikipedia pulls images that are stored on its sister site: Wikimedia Commons If you want to add an image to an article, it’s easiest if you can find images that are already available Wikimedia Commons. You can simply go to Insert: Media and search for images you’d like to add. You can also search Wikimedia Commons for images.
If you can’t find an already uploaded image, you can upload images to Wikimedia Commons. Importantly, copyright restrictions apply, and for the most part you will only be able to upload images you took yourself, not images that you have found on the web (with a few exceptions - see next section). If you have an image you took you can upload it in the visual editor, by clicking insert (also shown as a + icon): media, and then clicking the upload tab
You can upload free works to Wikimedia Commons and use them in your Wikipedia article. Free works are generally either:
Works in the public domain (that means created before 1926 in the United States - NOT that it is generally available on the internet). Find Public Domain works in digital libraries such as:
Works that have been made available under a Creative Commons license, you can search for cc-licensed images here:
If you are uploading free works (public domain or creative commons) upload your file to Wikimedia Commons here: Wikimedia Commons Uploader then you’ll be able to add it to your Wikipedia article like normal.
Wikipedia allows editors to claim Fair Use (the legal but unauthorized use of copyrighted material) in using images to illustrate articles. You can read about using non-free works under fair use here. In order to claim fair use these conditions should apply:
If you planning to claim fair use to use a non-free work you should upload it to Wikipedia here: Non-Free Image Uploader