Legally use photos in four ways: 1) find photos that are licensed as Creative Commons, 2) ask permission from the photographer, 3) buy photos from a stock photo site (e.g., istockphoto.com) or 4) take your own photos.
Look for larger image sizes, and do not increase the photo from the original size. Enlarging small photos will make them blurry.
Do not use an image as background (the text will be hard to read). Instead, use a background color and boxes to set off text and images.
If attending a conference outside the university, remember to identify yourself as an affiliate of the University of Tennessee. Visit UT's branding page for information on our color palette and styles.