After years of experience creating hundreds of websites, I've come to realize that there are two different types of images that you need when building a website.
The first type of images needed have to be excellent quality and are placed on the main pages of your website. These are pages like your homepage or any of your other main navigational pages.
For these types of images, I recommend that you use Shutterstock. I've personally used Shutterstock for years and really like them because the images are much more affordable (as low as $0.27) than some of the other providers out there.
Again, I only recommend that you purchase images for your homepage and navigational pages on your website. If you are looking for other images for blog posts/emails/social media, I advise you to look at the free resources below.
The second type of images needed are typically ones that you can throw on your blog posts, in your emails, on social media, and many other places where the quality and context has to be good, but not as good as those main website images.
These images are also important, but not as crucial as the first type of images because they are seen less and aren't as likely to be paid as much attention to. The below section is for those images.
The resources below are all CC0, meaning that they are public domain. You do not have to give attribution for any of these photos, you don't have to pay for them, and you don't have to give credit to anyone when using them. In other words, it is completely safe to Copy/Paste or download the photos from any of these websites as they are okay to use for personal or commercial use.
Pixabay: This is my go-to for website images as they have 500,000+ available.
PicJumbo: Though I am not sure of how many images this website has, there are a lot of good ones here as well.
LifeofPix: Another decent sized database of free images. These are also really high quality and although the organization of the website is a little meh, the images are pretty great.
Gratisography: These images have a certain photographic effect to them that make them look a little vintage, but still really high quality and sharp. A pretty good database here, and many of these images I haven't seen used in other places.
Unsplash: This platform lets you get ten free images ever ten days and has a searchable database. Though they don't have as many images as the other platforms, still worth checking out for sure!
Picography: Again, a little smaller than the first two options but some really great high quality photos here as well.
Cupcake: Another small database of free images, but still high quality and ones that will look great on your website.
DeathToTheStockPhoto: A neat little service that will send you high quality images every month. The problem with this website is it doesn't have a ready-made database, but it does have a lot of great images when they mail them out.
Google Advanced Image Search: Did you know that it IS possible to find images in Google through their image search? The process is actually pretty simple.
On the "Usage Rights" section, change the dropdown from "Not filtered by license" to "Free to use, share or modify, even commercially".
Flickr.com: One of the largest databases of free images is available on Flickr. However, not all images on Flickr are free to use commercially. Like Google, the user needs to go to an advanced search option and change the setting to find pictures that are okay to use. The process here is also simple.
On the Creative Commons section, check "Only search within Creative Commons-licensed content" and "Find content to use commercially"
Disclosure: Keep in mind that all of these websites were free when added to this list and could possibly change in the future. It is ultimately up to you to confirm that the images are free and I take no responsibility if these websites change policies and the images are no longer free. With that being said, I highly doubt this will occur, but I need to make sure to write this disclosure just in case.