Here are some of the best sites to get copyright/royalty free images to use for graphics. Links will be provided in an inline comment next to each site name.

1. pixabay

On this site you can find free vectors, illustrations, photos, videos and music to use for graphics. 

2. pexels

This is my favourite site to use as the photos are in great quality and they are not stock photos, so they're a lot more interesting and aesthetically pleasing.

3. freepik

This site is really similar to pixabay, but I find it much easier to navigate and it has a lot better content. Here you can find vectors, photos and photoshop files.

4. Unsplash

I do not use this site often but they have a wide variety of topics that you can look through for photos to use for free.

5. StockSnap.io

I also do not use this one that often, but they do have a lot of high quality photos and many categories to look through as well.

6. Adobe Stock

Adobe stock is not entirely free, but on the drop down section of the search bar you can look through their free resources. You can also sign up for a month free trial of 10 stock photos (which I did because their photos are really really good but super expensive, just remember to cancel your subscription).

7. DeviantArt

DeviantArt has a wide selection of different art, some of which users will allow you to use for free with or without credits (which you should read the description of the image before downloading so you know beforehand).