Aside from using your own photos, you can also use photos that you can find on the Internet. However, you have to make sure that you are legally allowed to use the photos that you are using. You can legally use photos that are in the public domain or that have a Creative Commons license. For Creative Commons licenses, you should use ones that are attribution (CC:BY), share-alike (CC:BY-SA), or no-derivs (CC:BY-ND). You can also use the ones that say non-commercial but only if your hubs aren't commercial.
If the pictures are in the public domain or have the creative commons license, you'll usually see this indicated in the photo or by going to the photo details. But photos which don't state that they are public domain or have the creative commons license means they are copyrighted and you shouldn't use those photos.
You can find photos that you can legally use on many sites such as flickr, Wikimedia Commons and pixabay.
For more information on this, you can check the learning center guide here on HubPages. Just click on the "help" link at the top of any HubPages page and you'll be taken to a page where you can see the link for the learning center. Once you click on that, you'll be taken to the learning center where you can find many helpful and useful information. Here's the link to the guide on proper image use - https://hubpageshelp.com/content/Learning-Center-l . Hope this helped.