1. How do I find free images online? When should I pay for images?
When you're using an image for a presentation, blog, or on social media, it's important to consider whether you need permission to use it. Consider searching for public domain or Creative Common images that are explicitly available for you to use for free; if these images don't meet your needs, consider licensing images.
Start with the assumption that all images are protected by copyright. Fair use may apply if the image is part of a larger work (such as one figure from an article), but using a whole image often won't fall under fair use.
Use photographs you have taken yourself. Unless you are taking photos as part of your job, you own the copyright for your own photos. (Don't forget to obtain a model release from any persons in your photographs. This is not a copyright issue but is a privacy issue).
Search for images with Creative Commons licenses or those in the public domain. In Google Images, change the Usage Rights settings under Tools to limit your search.
Purchase images from stock photo agencies and follow the license terms; you are not outright buying the image from a stock agency but are paying for certain uses of the image. Read the specific terms and conditions to see how you are permitted to use the image.
Seek permission directly from the copyright owner of an image; many will allow free use in non-commercial and educational works. Always ask first if they actually own the copyright in the image.
2. Where can I find medical images?