Looking for pictures that you can use on your website that are in the public domain? I Googled (it is a verb now) “pictures public domain wiki” and got a list of sites on this page: Wikipedia:Public domain image resources
The web site publicdomainpictures.net might be a good resource if you need pictures for your web site. Pixabay looks good also. WikiMedia Commons may be the best choice. It is discussed below.
If you go to the website and scroll down to the section on the right-hand side called Content and then pick a category, you can get the images. For example, click Animalia under the Nature category. This takes you to the Wikimedia Commons page called Category:Animalia. Scroll down this page until you get to the Subcategories section. Now, click on the link called Gallery of Animals in the G section. Scroll down and click on your favorite animal. If you pick Eagle and click on it you will see some pictures of eagles on the next page that appears. Click on one of the pictures. This takes you to a page with the picture taing up most of your screen. At the bottom of the picture there is blue button called More Details. Click it.
Again, a page opens up with the picture in it. On the right-hand side there is a link called Use this file on the web. Click it.
In the screenshot below you will see the two links I used to produce the content at the bottom of the page. I copied and pasted two of those links into this post. Below the picture is the attribution. The picture itself is displayed from the last one called HTML/BBCode. First, select he HTML radio button and if you wish you can select the size you want in the drop-down. Click the code. Copy and paste it into your website. Also copy and paste the Attribution text after you select the HTML checkbox to the right of it.