Stock art companies such as Getty Images and Shutterstock have collections of thousands of images and charge a fee by subscription or per image. Fees range based on the size of the image and how you want to use it; subscription-based services may offer discounted options, which could be beneficial if you need a number of images.
A selection of free photos is available from copyright-free stock sites such as Pixabay, which require photographers to waive copyright and related rights to videos and images they upload. This means users can copy, alter and distribute these images without credit to the photographers. In addition, the U.S. Department of Agriculture's National Agricultural Library offers free MyPlate graphics, health-related photographs and other artwork on its Professional and Career Resources web page.
If you stumble upon artwork on a personal or commercial website, you can try asking the owner of the image for permission to use it. Some amateur photographers don't mind lending an image as long as they receive credit. However, professional photographers are less likely to grant permission for free since their pictures are their livelihood. If you can't find the owner of the artwork, don't risk using it without permission.
Another possibility for those with an eye for composition and lighting is DIY photography, which allows you to easily create your own vision and style. Whether your camera is professional-grade, point-and-shoot or built into your phone, there are tons of hacks, tricks and mobile apps that can help you achieve high-quality imagery.