I use a lot of visuals in my work. I prefer to use my own photographs and to draw my own illustrations. When it's not practical or possible to use my own work, I rely on a handful of websites that provide copyright friendly images. Those images are licensed as public domain or Creative Commons Attribution.
Images that are licensed as public domain do not require any citation. When a creator gives his or her image a public domain license, he or she waives all rights to the image, including the right to attribution. A Creative Commons Zero License (CC0) is another way to state that the work has been put into the public domain.
Images with a Creative Commons Attribution (CC-BY) license can be shared and reused as long as attribution is given. There are other Creative Commons licenses that are more restrictive. They include ShareAlike, Noncommercial, and NoDerivatives.
The Noun Project has a huge collection of free symbols and icons. You can find clear and simple images to illustrate just about any idea. You have permission to use The Noun Project's images in your own projects because they are covered under a Creative Commons Attribution or a Public Domain license. If an attribution is required, the citation is attached to the downloaded image. Downloading from The Noun Project does require a free account, and downloading currently does not work on tablets or smartphones. Good news: The Noun Project's icons are no longer limited to black; a recent update now allows you to download any icon in any color!
Openclipart.org is filled with public domain graphics that you can freely use for any purpose. I often use images from Openclipart in my slideshows, infopgraphics, and posts. You can download any images from the site as a high resolution PNG (Portable Network Graphic). A PNG can have a transparent background and various levels of opacity, so your graphic will blend right into whatever project you’re using it for. You truly can use images from Openclipart for any purpose, and you can even make money off of what you create with their images. Here’s what the site says: “We try to make it clear that you may use all clipart from Openclipart even for unlimited commercial use. We believe that giving away our images is a great way to share with the world our talents and that will come back around in a better form.”
There are about 900 emoji characters and they are treated like text. If your computer or device doesn't have an emoji keyboard, you can search, copy and paste emoji characters from emojipedia.org. I like that Emojipedia tells me what each emoji is supposed to be. It also displays how emojis will look on different platforms.
AutoDraw.com is a free Google experiment. You simply do a quick sketch of an object, and AutoDraw guesses what you are trying to draw and suggests clipart. After you click a suggested drawing, your scribble is replaced with the artwork. You can use the Select tool to move, resize, and rotate the drawing. You recolor the illustrations by choosing a color in the Color Picker and then using the Fill Tool. AutoDraw is completely web-based and works on all kinds of devices: smartphones, tablets, laptops, and desktops. You can sketch with a touchscreen or draw using a mouse. AutoDraw’s library of illustrations does not have drawings for everything, but AutoDraw is accepting donations from artists, so we’ll see the collection of available illustrations increase over time. You’ll certainly find suggestions for drawings of ordinary objects like flowers, pizza, socks, and cake. I cannot find where Google mentions the license to AutoDraw's illustrations. It seems artists donate their drawings, but they are not labeled as public domain or Creative Commons.
Pixabay is filled with public domain photos and graphics that you can freely use for any purpose. You can download any photo from the site as a high resolution JPEG. Go ahead and log in to Pixabay to avoid those annoying squiggly letter captcha. Beware: Shutterstock advertisement on results pages can be easily confused with Pixabay's free images.
It can be a real pain to cite images. Photos for Class is here to help! This free site searches Creative Commons licensed images, and the images are filtered to be appropriate for school. Downloaded images have a black bar added to the bottom with the attribution. No copying, pasting, and keeping track of where to photo came from because that information is attached to the photo itself.
Pexels.com has high quality public domain (Creative Commons Zero License) stock photos that you can freely use for any purpose. Youdownload photos from the site as a high resolution JPEG and no logging in. Many of the photos on Pexels are also available on Pixabay.
Pond5 is a website that sells stock media for projects. However, they have a section with free historic photos and videos at pond5.com/free. In fact, the historic photos are licensed as public domain, so you can use them in any project, and you don’t have to include a citation. An account is required to download the free media. While each image’s details page has a download button, the downloaded photo is a somewhat low resolution version. You can usually get a much higher resolution version by adding it to your cart and checking out (for a total of $0).