Images and graphics give readers' eyes a break between text, helping them further engage with the content.
Raster graphics (.bmp, .jpg, .png, .gif, .tif, etc.) are based on a grid of pixels. The pixels represent colours that make up a bigger image and are resolution dependent. As a raster graphic is resized, eventually it will begin to look "pixelated" due to the pixels being “stretched” beyond their original size.
Tip: If using a raster image, use a large enough file size (resolution) so that the image will not look pixelated when resized.
Vector images (.ai, .eps, .svg, and some .pdf) are based on a mathematical equation. For example, if an image is a vector format circle, it is drawn by the computer from a mathematical formula. If you resize that circle by 1000x, the formula still calculates in correct proportion. This means that no matter how much you resize vector images they will scale properly and will not pixelate.
Remember that you need to cite any work created by others, including images, even if they are in the public domain. For information and examples of image citation in three different citation styles, see this guide from SFU Library.
Below are some suggested websites with searchable images. For each image you use, remember to check for a license stating that image can be freely used, then cite the image.
Unsplash: freely usable images searchable by keyword
Pixabay: free images and royalty-free stock images searchable by keyword
The Noun Project: searchable database of graphic icons and photos: many can be freely used
Google Images: do a search, then choose: Settings-->Advanced Search-->Usage Rights-->"Creative Commons licenses"
Wikimedia Commons: free media repository
Rijksmuseum Rijksstudio: art historical images
Example image license statements: Look for something like these so you know you are allowed to use an image freely.