Most are, but many of them carry Creative Commons licenses allowing many free uses. Copyright status is well marked on each file's page.
You can find images of bullfrogs on wikimedia commons.
Wikimedia Commons was created in 2004.
Search for images that are listed as "creative commons". You can find these types of images on Google or on sites like photopin.com
I would suggest Wikimedia Commons. If you follow the link below, you will find a wealth of links to subjects, each of which has links to medieval pictures.
One can find free baby images online through royalty-free stock photography sites such as Comstock and Wikimedia Commons, or on public photo sharing sites such as Flickr.
Wikimedia Commons has files with 11 different types of extensions available for use. Of those 11, they recommend, JPEG, SVG, PNG, or XCF. They do not allow BMP files.
they are copyrighted images to you are not allowed to copy them
Yes, but they are actually hosted on Wikimedia Commons, a freely licensed media site.
Wikimedia Commons is basically an international, open-source media repository. Media of all description (pictures, graphics, video and audio) are posted by the users/members; most works are original in nature and are shared under various license agreements (which the originator of the works selects when posting). In effect many of the pictures, maps and graphics that you will find embedded in Wikipedia are stored in Wikimedia Commons. Once registered, users can add, edit or append to existing media files.
I have put a few links to pictures of medieval cannon in Wikimedia Commons below:
Yes, wikipedia is a non-profit. Wikipedia is part of The Wikimedia Foundation Inc, which is a non-profit charitable organization, which also includes: Wikipedia, Wiktionary, Wikiquote, Wikibooks, Wikisource, Wikimedia Commons, Wikispecies, Wikinews, Wikiversity, Wikimedia Incubator and Meta-Wiki.
Public domain images have no copyright restrictions.Creative Commons images are protected by copyright, but have extremely broad licenses.