If the images in your presentation are your own intellectual property or are clip art that comes with the software, you can legally display them anywhere. If they are not, you need to cite their sources and obtain written permission. You have three choices for placing the source statements: at the bottom of the appropriate slides, in a sources slide that you show at the end of the presentation, or on a paper handout that you distribute at the end of the presentation.

Mobile Clinical Assistant: Courtesy of Panasonic Corporation.